base.js

// Copyright 2006 The Closure Library Authors. All Rights Reserved.
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
//      http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS-IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.

/**
 * @fileoverview Bootstrap for the Google JS Library (Closure).
 *
 * In uncompiled mode base.js will attempt to load Closure's deps file, unless
 * the global <code>CLOSURE_NO_DEPS</code> is set to true.  This allows projects
 * to include their own deps file(s) from different locations.
 *
 * Avoid including base.js more than once. This is strictly discouraged and not
 * supported. goog.require(...) won't work properly in that case.
 *
 * @provideGoog
 */


/**
 * @define {boolean} Overridden to true by the compiler.
 */
var COMPILED = false;


/**
 * Base namespace for the Closure library.  Checks to see goog is already
 * defined in the current scope before assigning to prevent clobbering if
 * base.js is loaded more than once.
 *
 * @const
 */
var goog = goog || {};

/**
 * Reference to the global context.  In most cases this will be 'window'.
 * @const
 * @suppress {newCheckTypes}
 */
goog.global = this;


/**
 * A hook for overriding the define values in uncompiled mode.
 *
 * In uncompiled mode, `CLOSURE_UNCOMPILED_DEFINES` may be defined before
 * loading base.js.  If a key is defined in `CLOSURE_UNCOMPILED_DEFINES`,
 * `goog.define` will use the value instead of the default value.  This
 * allows flags to be overwritten without compilation (this is normally
 * accomplished with the compiler's "define" flag).
 *
 * Example:
 * <pre>
 *   var CLOSURE_UNCOMPILED_DEFINES = {'goog.DEBUG': false};
 * </pre>
 *
 * @type {Object<string, (string|number|boolean)>|undefined}
 */
goog.global.CLOSURE_UNCOMPILED_DEFINES;


/**
 * A hook for overriding the define values in uncompiled or compiled mode,
 * like CLOSURE_UNCOMPILED_DEFINES but effective in compiled code.  In
 * uncompiled code CLOSURE_UNCOMPILED_DEFINES takes precedence.
 *
 * Also unlike CLOSURE_UNCOMPILED_DEFINES the values must be number, boolean or
 * string literals or the compiler will emit an error.
 *
 * While any @define value may be set, only those set with goog.define will be
 * effective for uncompiled code.
 *
 * Example:
 * <pre>
 *   var CLOSURE_DEFINES = {'goog.DEBUG': false} ;
 * </pre>
 *
 * @type {Object<string, (string|number|boolean)>|undefined}
 */
goog.global.CLOSURE_DEFINES;


/**
 * Returns true if the specified value is not undefined.
 *
 * @param {?} val Variable to test.
 * @return {boolean} Whether variable is defined.
 */
goog.isDef = function(val) {
  // void 0 always evaluates to undefined and hence we do not need to depend on
  // the definition of the global variable named 'undefined'.
  return val !== void 0;
};

/**
 * Returns true if the specified value is a string.
 * @param {?} val Variable to test.
 * @return {boolean} Whether variable is a string.
 */
goog.isString = function(val) {
  return typeof val == 'string';
};


/**
 * Returns true if the specified value is a boolean.
 * @param {?} val Variable to test.
 * @return {boolean} Whether variable is boolean.
 */
goog.isBoolean = function(val) {
  return typeof val == 'boolean';
};


/**
 * Returns true if the specified value is a number.
 * @param {?} val Variable to test.
 * @return {boolean} Whether variable is a number.
 */
goog.isNumber = function(val) {
  return typeof val == 'number';
};


/**
 * Builds an object structure for the provided namespace path, ensuring that
 * names that already exist are not overwritten. For example:
 * "a.b.c" -> a = {};a.b={};a.b.c={};
 * Used by goog.provide and goog.exportSymbol.
 * @param {string} name name of the object that this file defines.
 * @param {*=} opt_object the object to expose at the end of the path.
 * @param {Object=} opt_objectToExportTo The object to add the path to; default
 *     is `goog.global`.
 * @private
 */
goog.exportPath_ = function(name, opt_object, opt_objectToExportTo) {
  var parts = name.split('.');
  var cur = opt_objectToExportTo || goog.global;

  // Internet Explorer exhibits strange behavior when throwing errors from
  // methods externed in this manner.  See the testExportSymbolExceptions in
  // base_test.html for an example.
  if (!(parts[0] in cur) && typeof cur.execScript != 'undefined') {
    cur.execScript('var ' + parts[0]);
  }

  for (var part; parts.length && (part = parts.shift());) {
    if (!parts.length && goog.isDef(opt_object)) {
      // last part and we have an object; use it
      cur[part] = opt_object;
    } else if (cur[part] && cur[part] !== Object.prototype[part]) {
      cur = cur[part];
    } else {
      cur = cur[part] = {};
    }
  }
};


/**
 * Defines a named value. In uncompiled mode, the value is retrieved from
 * CLOSURE_DEFINES or CLOSURE_UNCOMPILED_DEFINES if the object is defined and
 * has the property specified, and otherwise used the defined defaultValue.
 * When compiled the default can be overridden using the compiler
 * options or the value set in the CLOSURE_DEFINES object.
 *
 * @param {string} name The distinguished name to provide.
 * @param {string|number|boolean} defaultValue
 */
goog.define = function(name, defaultValue) {
  var value = defaultValue;
  if (!COMPILED) {
    var uncompiledDefines = goog.global.CLOSURE_UNCOMPILED_DEFINES;
    var defines = goog.global.CLOSURE_DEFINES;
    if (uncompiledDefines &&
        // Anti DOM-clobbering runtime check (b/37736576).
        /** @type {?} */ (uncompiledDefines).nodeType === undefined &&
        Object.prototype.hasOwnProperty.call(uncompiledDefines, name)) {
      value = uncompiledDefines[name];
    } else if (
        defines &&
        // Anti DOM-clobbering runtime check (b/37736576).
        /** @type {?} */ (defines).nodeType === undefined &&
        Object.prototype.hasOwnProperty.call(defines, name)) {
      value = defines[name];
    }
  }
  goog.exportPath_(name, value);
};


/**
 * @define {boolean} DEBUG is provided as a convenience so that debugging code
 * that should not be included in a production. It can be easily stripped
 * by specifying --define goog.DEBUG=false to the Closure Compiler aka
 * JSCompiler. For example, most toString() methods should be declared inside an
 * "if (goog.DEBUG)" conditional because they are generally used for debugging
 * purposes and it is difficult for the JSCompiler to statically determine
 * whether they are used.
 */
goog.define('goog.DEBUG', true);


/**
 * @define {string} LOCALE defines the locale being used for compilation. It is
 * used to select locale specific data to be compiled in js binary. BUILD rule
 * can specify this value by "--define goog.LOCALE=<locale_name>" as a compiler
 * option.
 *
 * Take into account that the locale code format is important. You should use
 * the canonical Unicode format with hyphen as a delimiter. Language must be
 * lowercase, Language Script - Capitalized, Region - UPPERCASE.
 * There are few examples: pt-BR, en, en-US, sr-Latin-BO, zh-Hans-CN.
 *
 * See more info about locale codes here:
 * http://www.unicode.org/reports/tr35/#Unicode_Language_and_Locale_Identifiers
 *
 * For language codes you should use values defined by ISO 693-1. See it here
 * http://www.w3.org/WAI/ER/IG/ert/iso639.htm. There is only one exception from
 * this rule: the Hebrew language. For legacy reasons the old code (iw) should
 * be used instead of the new code (he).
 *
 */
goog.define('goog.LOCALE', 'en');  // default to en


/**
 * @define {boolean} Whether this code is running on trusted sites.
 *
 * On untrusted sites, several native functions can be defined or overridden by
 * external libraries like Prototype, Datejs, and JQuery and setting this flag
 * to false forces closure to use its own implementations when possible.
 *
 * If your JavaScript can be loaded by a third party site and you are wary about
 * relying on non-standard implementations, specify
 * "--define goog.TRUSTED_SITE=false" to the compiler.
 */
goog.define('goog.TRUSTED_SITE', true);


/**
 * @define {boolean} Whether a project is expected to be running in strict mode.
 *
 * This define can be used to trigger alternate implementations compatible with
 * running in EcmaScript Strict mode or warn about unavailable functionality.
 * @see https://goo.gl/PudQ4y
 *
 */
goog.define('goog.STRICT_MODE_COMPATIBLE', false);


/**
 * @define {boolean} Whether code that calls {@link goog.setTestOnly} should
 *     be disallowed in the compilation unit.
 */
goog.define('goog.DISALLOW_TEST_ONLY_CODE', COMPILED && !goog.DEBUG);


/**
 * @define {boolean} Whether to use a Chrome app CSP-compliant method for
 *     loading scripts via goog.require. @see appendScriptSrcNode_.
 */
goog.define('goog.ENABLE_CHROME_APP_SAFE_SCRIPT_LOADING', false);


/**
 * Defines a namespace in Closure.
 *
 * A namespace may only be defined once in a codebase. It may be defined using
 * goog.provide() or goog.module().
 *
 * The presence of one or more goog.provide() calls in a file indicates
 * that the file defines the given objects/namespaces.
 * Provided symbols must not be null or undefined.
 *
 * In addition, goog.provide() creates the object stubs for a namespace
 * (for example, goog.provide("goog.foo.bar") will create the object
 * goog.foo.bar if it does not already exist).
 *
 * Build tools also scan for provide/require/module statements
 * to discern dependencies, build dependency files (see deps.js), etc.
 *
 * @see goog.require
 * @see goog.module
 * @param {string} name Namespace provided by this file in the form
 *     "goog.package.part".
 */
goog.provide = function(name) {
  if (goog.isInModuleLoader_()) {
    throw new Error('goog.provide cannot be used within a module.');
  }
  if (!COMPILED) {
    // Ensure that the same namespace isn't provided twice.
    // A goog.module/goog.provide maps a goog.require to a specific file
    if (goog.isProvided_(name)) {
      throw new Error('Namespace "' + name + '" already declared.');
    }
  }

  goog.constructNamespace_(name);
};


/**
 * @param {string} name Namespace provided by this file in the form
 *     "goog.package.part".
 * @param {Object=} opt_obj The object to embed in the namespace.
 * @private
 */
goog.constructNamespace_ = function(name, opt_obj) {
  if (!COMPILED) {
    delete goog.implicitNamespaces_[name];

    var namespace = name;
    while ((namespace = namespace.substring(0, namespace.lastIndexOf('.')))) {
      if (goog.getObjectByName(namespace)) {
        break;
      }
      goog.implicitNamespaces_[namespace] = true;
    }
  }

  goog.exportPath_(name, opt_obj);
};


/**
 * Returns CSP nonce, if set for any script tag.
 * @param {?Window=} opt_window The window context used to retrieve the nonce.
 *     Defaults to global context.
 * @return {string} CSP nonce or empty string if no nonce is present.
 */
goog.getScriptNonce = function(opt_window) {
  if (opt_window && opt_window != goog.global) {
    return goog.getScriptNonce_(opt_window.document);
  }
  if (goog.cspNonce_ === null) {
    goog.cspNonce_ = goog.getScriptNonce_(goog.global.document);
  }
  return goog.cspNonce_;
};


/**
 * According to the CSP3 spec a nonce must be a valid base64 string.
 * @see https://www.w3.org/TR/CSP3/#grammardef-base64-value
 * @private @const
 */
goog.NONCE_PATTERN_ = /^[\w+/_-]+[=]{0,2}$/;


/**
 * @private {?string}
 */
goog.cspNonce_ = null;


/**
 * Returns CSP nonce, if set for any script tag.
 * @param {!Document} doc
 * @return {string} CSP nonce or empty string if no nonce is present.
 * @private
 */
goog.getScriptNonce_ = function(doc) {
  var script = doc.querySelector && doc.querySelector('script[nonce]');
  if (script) {
    // Try to get the nonce from the IDL property first, because browsers that
    // implement additional nonce protection features (currently only Chrome) to
    // prevent nonce stealing via CSS do not expose the nonce via attributes.
    // See https://github.com/whatwg/html/issues/2369
    var nonce = script['nonce'] || script.getAttribute('nonce');
    if (nonce && goog.NONCE_PATTERN_.test(nonce)) {
      return nonce;
    }
  }
  return '';
};


/**
 * Module identifier validation regexp.
 * Note: This is a conservative check, it is very possible to be more lenient,
 *   the primary exclusion here is "/" and "\" and a leading ".", these
 *   restrictions are intended to leave the door open for using goog.require
 *   with relative file paths rather than module identifiers.
 * @private
 */
goog.VALID_MODULE_RE_ = /^[a-zA-Z_$][a-zA-Z0-9._$]*$/;


/**
 * Defines a module in Closure.
 *
 * Marks that this file must be loaded as a module and claims the namespace.
 *
 * A namespace may only be defined once in a codebase. It may be defined using
 * goog.provide() or goog.module().
 *
 * goog.module() has three requirements:
 * - goog.module may not be used in the same file as goog.provide.
 * - goog.module must be the first statement in the file.
 * - only one goog.module is allowed per file.
 *
 * When a goog.module annotated file is loaded, it is enclosed in
 * a strict function closure. This means that:
 * - any variables declared in a goog.module file are private to the file
 * (not global), though the compiler is expected to inline the module.
 * - The code must obey all the rules of "strict" JavaScript.
 * - the file will be marked as "use strict"
 *
 * NOTE: unlike goog.provide, goog.module does not declare any symbols by
 * itself. If declared symbols are desired, use
 * goog.module.declareLegacyNamespace().
 *
 *
 * See the public goog.module proposal: http://goo.gl/Va1hin
 *
 * @param {string} name Namespace provided by this file in the form
 *     "goog.package.part", is expected but not required.
 * @return {void}
 */
goog.module = function(name) {
  if (!goog.isString(name) || !name ||
      name.search(goog.VALID_MODULE_RE_) == -1) {
    throw new Error('Invalid module identifier');
  }
  if (!goog.isInGoogModuleLoader_()) {
    throw new Error(
        'Module ' + name + ' has been loaded incorrectly. Note, ' +
        'modules cannot be loaded as normal scripts. They require some kind of ' +
        'pre-processing step. You\'re likely trying to load a module via a ' +
        'script tag or as a part of a concatenated bundle without rewriting the ' +
        'module. For more info see: ' +
        'https://github.com/google/closure-library/wiki/goog.module:-an-ES6-module-like-alternative-to-goog.provide.');
  }
  if (goog.moduleLoaderState_.moduleName) {
    throw new Error('goog.module may only be called once per module.');
  }

  // Store the module name for the loader.
  goog.moduleLoaderState_.moduleName = name;
  if (!COMPILED) {
    // Ensure that the same namespace isn't provided twice.
    // A goog.module/goog.provide maps a goog.require to a specific file
    if (goog.isProvided_(name)) {
      throw new Error('Namespace "' + name + '" already declared.');
    }
    delete goog.implicitNamespaces_[name];
  }
};


/**
 * @param {string} name The module identifier.
 * @return {?} The module exports for an already loaded module or null.
 *
 * Note: This is not an alternative to goog.require, it does not
 * indicate a hard dependency, instead it is used to indicate
 * an optional dependency or to access the exports of a module
 * that has already been loaded.
 * @suppress {missingProvide}
 */
goog.module.get = function(name) {

  return goog.module.getInternal_(name);
};


/**
 * @param {string} name The module identifier.
 * @return {?} The module exports for an already loaded module or null.
 * @private
 */
goog.module.getInternal_ = function(name) {
  if (!COMPILED) {
    if (name in goog.loadedModules_) {
      return goog.loadedModules_[name].exports;
    } else if (!goog.implicitNamespaces_[name]) {
      var ns = goog.getObjectByName(name);
      return ns != null ? ns : null;
    }
  }
  return null;
};


/**
 * Types of modules the debug loader can load.
 * @enum {string}
 */
goog.ModuleType = {
  ES6: 'es6',
  GOOG: 'goog'
};


/**
 * @private {?{
 *   moduleName: (string|undefined),
 *   declareLegacyNamespace:boolean,
 *   type: ?goog.ModuleType
 * }}
 */
goog.moduleLoaderState_ = null;


/**
 * @private
 * @return {boolean} Whether a goog.module or an es6 module is currently being
 *     initialized.
 */
goog.isInModuleLoader_ = function() {
  return goog.isInGoogModuleLoader_() || goog.isInEs6ModuleLoader_();
};


/**
 * @private
 * @return {boolean} Whether a goog.module is currently being initialized.
 */
goog.isInGoogModuleLoader_ = function() {
  return !!goog.moduleLoaderState_ &&
      goog.moduleLoaderState_.type == goog.ModuleType.GOOG;
};


/**
 * @private
 * @return {boolean} Whether an es6 module is currently being initialized.
 */
goog.isInEs6ModuleLoader_ = function() {
  var inLoader = !!goog.moduleLoaderState_ &&
      goog.moduleLoaderState_.type == goog.ModuleType.ES6;

  if (inLoader) {
    return true;
  }

  var jscomp = goog.global['$jscomp'];

  if (jscomp) {
    // jscomp may not have getCurrentModulePath if this is a compiled bundle
    // that has some of the runtime, but not all of it. This can happen if
    // optimizations are turned on so the unused runtime is removed but renaming
    // and Closure pass are off (so $jscomp is still named $jscomp and the
    // goog.provide/require calls still exist).
    if (typeof jscomp.getCurrentModulePath != 'function') {
      return false;
    }

    // Bundled ES6 module.
    return !!jscomp.getCurrentModulePath();
  }

  return false;
};


/**
 * Provide the module's exports as a globally accessible object under the
 * module's declared name.  This is intended to ease migration to goog.module
 * for files that have existing usages.
 * @suppress {missingProvide}
 */
goog.module.declareLegacyNamespace = function() {
  if (!COMPILED && !goog.isInGoogModuleLoader_()) {
    throw new Error(
        'goog.module.declareLegacyNamespace must be called from ' +
        'within a goog.module');
  }
  if (!COMPILED && !goog.moduleLoaderState_.moduleName) {
    throw new Error(
        'goog.module must be called prior to ' +
        'goog.module.declareLegacyNamespace.');
  }
  goog.moduleLoaderState_.declareLegacyNamespace = true;
};


/**
 * Associates an ES6 module with a Closure module ID so that is available via
 * goog.require. The associated ID  acts like a goog.module ID - it does not
 * create any global names, it is merely available via goog.require /
 * goog.module.get / goog.forwardDeclare / goog.requireType. goog.require and
 * goog.module.get will return the entire module as if it was import *'d. This
 * allows Closure files to reference ES6 modules for the sake of migration.
 *
 * @param {string} namespace
 * @suppress {missingProvide}
 */
goog.declareModuleId = function(namespace) {
  if (!COMPILED) {
    if (!goog.isInEs6ModuleLoader_()) {
      throw new Error(
          'goog.declareModuleId may only be called from ' +
          'within an ES6 module');
    }
    if (goog.moduleLoaderState_ && goog.moduleLoaderState_.moduleName) {
      throw new Error(
          'goog.declareModuleId may only be called once per module.');
    }
    if (namespace in goog.loadedModules_) {
      throw new Error(
          'Module with namespace "' + namespace + '" already exists.');
    }
  }
  if (goog.moduleLoaderState_) {
    // Not bundled - debug loading.
    goog.moduleLoaderState_.moduleName = namespace;
  } else {
    // Bundled - not debug loading, no module loader state.
    var jscomp = goog.global['$jscomp'];
    if (!jscomp || typeof jscomp.getCurrentModulePath != 'function') {
      throw new Error(
          'Module with namespace "' + namespace +
          '" has been loaded incorrectly.');
    }
    var exports = jscomp.require(jscomp.getCurrentModulePath());
    goog.loadedModules_[namespace] = {
      exports: exports,
      type: goog.ModuleType.ES6,
      moduleId: namespace
    };
  }
};


/**
 * Deprecated old name for goog.declareModuleId. This function is being renamed
 * to help disambiguate with goog.module.declareLegacyNamespace.
 *
 * @type {function(string): undefined}
 * @suppress {missingProvide}
 */
goog.module.declareNamespace = goog.declareModuleId;


/**
 * Marks that the current file should only be used for testing, and never for
 * live code in production.
 *
 * In the case of unit tests, the message may optionally be an exact namespace
 * for the test (e.g. 'goog.stringTest'). The linter will then ignore the extra
 * provide (if not explicitly defined in the code).
 *
 * @param {string=} opt_message Optional message to add to the error that's
 *     raised when used in production code.
 */
goog.setTestOnly = function(opt_message) {
  if (goog.DISALLOW_TEST_ONLY_CODE) {
    opt_message = opt_message || '';
    throw new Error(
        'Importing test-only code into non-debug environment' +
        (opt_message ? ': ' + opt_message : '.'));
  }
};


/**
 * Forward declares a symbol. This is an indication to the compiler that the
 * symbol may be used in the source yet is not required and may not be provided
 * in compilation.
 *
 * The most common usage of forward declaration is code that takes a type as a
 * function parameter but does not need to require it. By forward declaring
 * instead of requiring, no hard dependency is made, and (if not required
 * elsewhere) the namespace may never be required and thus, not be pulled
 * into the JavaScript binary. If it is required elsewhere, it will be type
 * checked as normal.
 *
 * Before using goog.forwardDeclare, please read the documentation at
 * https://github.com/google/closure-compiler/wiki/Bad-Type-Annotation to
 * understand the options and tradeoffs when working with forward declarations.
 *
 * @param {string} name The namespace to forward declare in the form of
 *     "goog.package.part".
 */
goog.forwardDeclare = function(name) {};


/**
 * Forward declare type information. Used to assign types to goog.global
 * referenced object that would otherwise result in unknown type references
 * and thus block property disambiguation.
 */
goog.forwardDeclare('Document');
goog.forwardDeclare('HTMLScriptElement');
goog.forwardDeclare('XMLHttpRequest');


if (!COMPILED) {
  /**
   * Check if the given name has been goog.provided. This will return false for
   * names that are available only as implicit namespaces.
   * @param {string} name name of the object to look for.
   * @return {boolean} Whether the name has been provided.
   * @private
   */
  goog.isProvided_ = function(name) {
    return (name in goog.loadedModules_) ||
        (!goog.implicitNamespaces_[name] &&
         goog.isDefAndNotNull(goog.getObjectByName(name)));
  };

  /**
   * Namespaces implicitly defined by goog.provide. For example,
   * goog.provide('goog.events.Event') implicitly declares that 'goog' and
   * 'goog.events' must be namespaces.
   *
   * @type {!Object<string, (boolean|undefined)>}
   * @private
   */
  goog.implicitNamespaces_ = {'goog.module': true};

  // NOTE: We add goog.module as an implicit namespace as goog.module is defined
  // here and because the existing module package has not been moved yet out of
  // the goog.module namespace. This satisifies both the debug loader and
  // ahead-of-time dependency management.
}


/**
 * Returns an object based on its fully qualified external name.  The object
 * is not found if null or undefined.  If you are using a compilation pass that
 * renames property names beware that using this function will not find renamed
 * properties.
 *
 * @param {string} name The fully qualified name.
 * @param {Object=} opt_obj The object within which to look; default is
 *     |goog.global|.
 * @return {?} The value (object or primitive) or, if not found, null.
 */
goog.getObjectByName = function(name, opt_obj) {
  var parts = name.split('.');
  var cur = opt_obj || goog.global;
  for (var i = 0; i < parts.length; i++) {
    cur = cur[parts[i]];
    if (!goog.isDefAndNotNull(cur)) {
      return null;
    }
  }
  return cur;
};


/**
 * Globalizes a whole namespace, such as goog or goog.lang.
 *
 * @param {!Object} obj The namespace to globalize.
 * @param {Object=} opt_global The object to add the properties to.
 * @deprecated Properties may be explicitly exported to the global scope, but
 *     this should no longer be done in bulk.
 */
goog.globalize = function(obj, opt_global) {
  var global = opt_global || goog.global;
  for (var x in obj) {
    global[x] = obj[x];
  }
};


/**
 * Adds a dependency from a file to the files it requires.
 * @param {string} relPath The path to the js file.
 * @param {!Array<string>} provides An array of strings with
 *     the names of the objects this file provides.
 * @param {!Array<string>} requires An array of strings with
 *     the names of the objects this file requires.
 * @param {boolean|!Object<string>=} opt_loadFlags Parameters indicating
 *     how the file must be loaded.  The boolean 'true' is equivalent
 *     to {'module': 'goog'} for backwards-compatibility.  Valid properties
 *     and values include {'module': 'goog'} and {'lang': 'es6'}.
 */
goog.addDependency = function(relPath, provides, requires, opt_loadFlags) {
  if (!COMPILED && goog.DEPENDENCIES_ENABLED) {
    goog.debugLoader_.addDependency(relPath, provides, requires, opt_loadFlags);
  }
};




// NOTE(nnaze): The debug DOM loader was included in base.js as an original way
// to do "debug-mode" development.  The dependency system can sometimes be
// confusing, as can the debug DOM loader's asynchronous nature.
//
// With the DOM loader, a call to goog.require() is not blocking -- the script
// will not load until some point after the current script.  If a namespace is
// needed at runtime, it needs to be defined in a previous script, or loaded via
// require() with its registered dependencies.
//
// User-defined namespaces may need their own deps file. For a reference on
// creating a deps file, see:
// Externally: https://developers.google.com/closure/library/docs/depswriter
//
// Because of legacy clients, the DOM loader can't be easily removed from
// base.js.  Work was done to make it disableable or replaceable for
// different environments (DOM-less JavaScript interpreters like Rhino or V8,
// for example). See bootstrap/ for more information.


/**
 * @define {boolean} Whether to enable the debug loader.
 *
 * If enabled, a call to goog.require() will attempt to load the namespace by
 * appending a script tag to the DOM (if the namespace has been registered).
 *
 * If disabled, goog.require() will simply assert that the namespace has been
 * provided (and depend on the fact that some outside tool correctly ordered
 * the script).
 */
goog.define('goog.ENABLE_DEBUG_LOADER', true);


/**
 * @param {string} msg
 * @private
 */
goog.logToConsole_ = function(msg) {
  if (goog.global.console) {
    goog.global.console['error'](msg);
  }
};


/**
 * Implements a system for the dynamic resolution of dependencies that works in
 * parallel with the BUILD system.
 *
 * Note that all calls to goog.require will be stripped by the compiler.
 *
 * @see goog.provide
 * @param {string} namespace Namespace (as was given in goog.provide,
 *     goog.module, or goog.declareModuleId) in the form
 *     "goog.package.part".
 * @return {?} If called within a goog.module or ES6 module file, the associated
 *     namespace or module otherwise null.
 */
goog.require = function(namespace) {
  if (!COMPILED) {
    // Might need to lazy load on old IE.
    if (goog.ENABLE_DEBUG_LOADER) {
      goog.debugLoader_.requested(namespace);
    }

    // If the object already exists we do not need to do anything.
    if (goog.isProvided_(namespace)) {
      if (goog.isInModuleLoader_()) {
        return goog.module.getInternal_(namespace);
      }
    } else if (goog.ENABLE_DEBUG_LOADER) {
      var moduleLoaderState = goog.moduleLoaderState_;
      goog.moduleLoaderState_ = null;
      try {
        goog.debugLoader_.load_(namespace);
      } finally {
        goog.moduleLoaderState_ = moduleLoaderState;
      }
    }

    return null;
  }
};


/**
 * Requires a symbol for its type information. This is an indication to the
 * compiler that the symbol may appear in type annotations, yet it is not
 * referenced at runtime.
 *
 * When called within a goog.module or ES6 module file, the return value may be
 * assigned to or destructured into a variable, but it may not be otherwise used
 * in code outside of a type annotation.
 *
 * Note that all calls to goog.requireType will be stripped by the compiler.
 *
 * @param {string} namespace Namespace (as was given in goog.provide,
 *     goog.module, or goog.declareModuleId) in the form
 *     "goog.package.part".
 * @return {?}
 */
goog.requireType = function(namespace) {
  // Return an empty object so that single-level destructuring of the return
  // value doesn't crash at runtime when using the debug loader. Multi-level
  // destructuring isn't supported.
  return {};
};


/**
 * Path for included scripts.
 * @type {string}
 */
goog.basePath = '';


/**
 * A hook for overriding the base path.
 * @type {string|undefined}
 */
goog.global.CLOSURE_BASE_PATH;


/**
 * Whether to attempt to load Closure's deps file. By default, when uncompiled,
 * deps files will attempt to be loaded.
 * @type {boolean|undefined}
 */
goog.global.CLOSURE_NO_DEPS;


/**
 * A function to import a single script. This is meant to be overridden when
 * Closure is being run in non-HTML contexts, such as web workers. It's defined
 * in the global scope so that it can be set before base.js is loaded, which
 * allows deps.js to be imported properly.
 *
 * The first parameter the script source, which is a relative URI. The second,
 * optional parameter is the script contents, in the event the script needed
 * transformation. It should return true if the script was imported, false
 * otherwise.
 * @type {(function(string, string=): boolean)|undefined}
 */
goog.global.CLOSURE_IMPORT_SCRIPT;


/**
 * Null function used for default values of callbacks, etc.
 * @return {void} Nothing.
 */
goog.nullFunction = function() {};


/**
 * When defining a class Foo with an abstract method bar(), you can do:
 * Foo.prototype.bar = goog.abstractMethod
 *
 * Now if a subclass of Foo fails to override bar(), an error will be thrown
 * when bar() is invoked.
 *
 * @type {!Function}
 * @throws {Error} when invoked to indicate the method should be overridden.
 */
goog.abstractMethod = function() {
  throw new Error('unimplemented abstract method');
};


/**
 * Adds a `getInstance` static method that always returns the same
 * instance object.
 * @param {!Function} ctor The constructor for the class to add the static
 *     method to.
 * @suppress {missingProperties} 'instance_' isn't a property on 'Function'
 *     but we don't have a better type to use here.
 */
goog.addSingletonGetter = function(ctor) {
  // instance_ is immediately set to prevent issues with sealed constructors
  // such as are encountered when a constructor is returned as the export object
  // of a goog.module in unoptimized code.
  // Delcare type to avoid conformance violations that ctor.instance_ is unknown
  /** @type {undefined|!Object} @suppress {underscore} */
  ctor.instance_ = undefined;
  ctor.getInstance = function() {
    if (ctor.instance_) {
      return ctor.instance_;
    }
    if (goog.DEBUG) {
      // NOTE: JSCompiler can't optimize away Array#push.
      goog.instantiatedSingletons_[goog.instantiatedSingletons_.length] = ctor;
    }
    // Cast to avoid conformance violations that ctor.instance_ is unknown
    return /** @type {!Object|undefined} */ (ctor.instance_) = new ctor;
  };
};


/**
 * All singleton classes that have been instantiated, for testing. Don't read
 * it directly, use the `goog.testing.singleton` module. The compiler
 * removes this variable if unused.
 * @type {!Array<!Function>}
 * @private
 */
goog.instantiatedSingletons_ = [];


/**
 * @define {boolean} Whether to load goog.modules using `eval` when using
 * the debug loader.  This provides a better debugging experience as the
 * source is unmodified and can be edited using Chrome Workspaces or similar.
 * However in some environments the use of `eval` is banned
 * so we provide an alternative.
 */
goog.define('goog.LOAD_MODULE_USING_EVAL', true);


/**
 * @define {boolean} Whether the exports of goog.modules should be sealed when
 * possible.
 */
goog.define('goog.SEAL_MODULE_EXPORTS', goog.DEBUG);


/**
 * The registry of initialized modules:
 * The module identifier or path to module exports map.
 * @private @const {!Object<string, {exports:?,type:string,moduleId:string}>}
 */
goog.loadedModules_ = {};


/**
 * True if the debug loader enabled and used.
 * @const {boolean}
 */
goog.DEPENDENCIES_ENABLED = !COMPILED && goog.ENABLE_DEBUG_LOADER;


/**
 * @define {string} How to decide whether to transpile.  Valid values
 * are 'always', 'never', and 'detect'.  The default ('detect') is to
 * use feature detection to determine which language levels need
 * transpilation.
 */
// NOTE(sdh): we could expand this to accept a language level to bypass
// detection: e.g. goog.TRANSPILE == 'es5' would transpile ES6 files but
// would leave ES3 and ES5 files alone.
goog.define('goog.TRANSPILE', 'detect');


/**
 * @define {string} If a file needs to be transpiled what the output language
 * should be. By default this is the highest language level this file detects
 * the current environment supports. Generally this flag should not be set, but
 * it could be useful to override. Example: If the current environment supports
 * ES6 then by default ES7+ files will be transpiled to ES6, unless this is
 * overridden.
 *
 * Valid values include: es3, es5, es6, es7, and es8. Anything not recognized
 * is treated as es3.
 *
 * Note that setting this value does not force transpilation. Just if
 * transpilation occurs this will be the output. So this is most useful when
 * goog.TRANSPILE is set to 'always' and then forcing the language level to be
 * something lower than what the environment detects.
 */
goog.define('goog.TRANSPILE_TO_LANGUAGE', '');


/**
 * @define {string} Path to the transpiler.  Executing the script at this
 * path (relative to base.js) should define a function $jscomp.transpile.
 */
goog.define('goog.TRANSPILER', 'transpile.js');


/**
 * @package {?boolean}
 * Visible for testing.
 */
goog.hasBadLetScoping = null;


/**
 * @return {boolean}
 * @package Visible for testing.
 */
goog.useSafari10Workaround = function() {
  if (goog.hasBadLetScoping == null) {
    var hasBadLetScoping;
    try {
      hasBadLetScoping = !eval(
          '"use strict";' +
          'let x = 1; function f() { return typeof x; };' +
          'f() == "number";');
    } catch (e) {
      // Assume that ES6 syntax isn't supported.
      hasBadLetScoping = false;
    }
    goog.hasBadLetScoping = hasBadLetScoping;
  }
  return goog.hasBadLetScoping;
};


/**
 * @param {string} moduleDef
 * @return {string}
 * @package Visible for testing.
 */
goog.workaroundSafari10EvalBug = function(moduleDef) {
  return '(function(){' + moduleDef +
      '\n' +  // Terminate any trailing single line comment.
      ';' +   // Terminate any trailing expression.
      '})();\n';
};


/**
 * @param {function(?):?|string} moduleDef The module definition.
 */
goog.loadModule = function(moduleDef) {
  // NOTE: we allow function definitions to be either in the from
  // of a string to eval (which keeps the original source intact) or
  // in a eval forbidden environment (CSP) we allow a function definition
  // which in its body must call `goog.module`, and return the exports
  // of the module.
  var previousState = goog.moduleLoaderState_;
  try {
    goog.moduleLoaderState_ = {
      moduleName: '',
      declareLegacyNamespace: false,
      type: goog.ModuleType.GOOG
    };
    var exports;
    if (goog.isFunction(moduleDef)) {
      exports = moduleDef.call(undefined, {});
    } else if (goog.isString(moduleDef)) {
      if (goog.useSafari10Workaround()) {
        moduleDef = goog.workaroundSafari10EvalBug(moduleDef);
      }

      exports = goog.loadModuleFromSource_.call(undefined, moduleDef);
    } else {
      throw new Error('Invalid module definition');
    }

    var moduleName = goog.moduleLoaderState_.moduleName;
    if (goog.isString(moduleName) && moduleName) {
      // Don't seal legacy namespaces as they may be used as a parent of
      // another namespace
      if (goog.moduleLoaderState_.declareLegacyNamespace) {
        goog.constructNamespace_(moduleName, exports);
      } else if (
          goog.SEAL_MODULE_EXPORTS && Object.seal &&
          typeof exports == 'object' && exports != null) {
        Object.seal(exports);
      }

      var data = {
        exports: exports,
        type: goog.ModuleType.GOOG,
        moduleId: goog.moduleLoaderState_.moduleName
      };
      goog.loadedModules_[moduleName] = data;
    } else {
      throw new Error('Invalid module name \"' + moduleName + '\"');
    }
  } finally {
    goog.moduleLoaderState_ = previousState;
  }
};


/**
 * @private @const
 */
goog.loadModuleFromSource_ = /** @type {function(string):?} */ (function() {
  // NOTE: we avoid declaring parameters or local variables here to avoid
  // masking globals or leaking values into the module definition.
  'use strict';
  var exports = {};
  eval(arguments[0]);
  return exports;
});


/**
 * Normalize a file path by removing redundant ".." and extraneous "." file
 * path components.
 * @param {string} path
 * @return {string}
 * @private
 */
goog.normalizePath_ = function(path) {
  var components = path.split('/');
  var i = 0;
  while (i < components.length) {
    if (components[i] == '.') {
      components.splice(i, 1);
    } else if (
        i && components[i] == '..' && components[i - 1] &&
        components[i - 1] != '..') {
      components.splice(--i, 2);
    } else {
      i++;
    }
  }
  return components.join('/');
};


/**
 * Provides a hook for loading a file when using Closure's goog.require() API
 * with goog.modules.  In particular this hook is provided to support Node.js.
 *
 * @type {(function(string):string)|undefined}
 */
goog.global.CLOSURE_LOAD_FILE_SYNC;


/**
 * Loads file by synchronous XHR. Should not be used in production environments.
 * @param {string} src Source URL.
 * @return {?string} File contents, or null if load failed.
 * @private
 */
goog.loadFileSync_ = function(src) {
  if (goog.global.CLOSURE_LOAD_FILE_SYNC) {
    return goog.global.CLOSURE_LOAD_FILE_SYNC(src);
  } else {
    try {
      /** @type {XMLHttpRequest} */
      var xhr = new goog.global['XMLHttpRequest']();
      xhr.open('get', src, false);
      xhr.send();
      // NOTE: Successful http: requests have a status of 200, but successful
      // file: requests may have a status of zero.  Any other status, or a
      // thrown exception (particularly in case of file: requests) indicates
      // some sort of error, which we treat as a missing or unavailable file.
      return xhr.status == 0 || xhr.status == 200 ? xhr.responseText : null;
    } catch (err) {
      // No need to rethrow or log, since errors should show up on their own.
      return null;
    }
  }
};


/**
 * Lazily retrieves the transpiler and applies it to the source.
 * @param {string} code JS code.
 * @param {string} path Path to the code.
 * @param {string} target Language level output.
 * @return {string} The transpiled code.
 * @private
 */
goog.transpile_ = function(code, path, target) {
  var jscomp = goog.global['$jscomp'];
  if (!jscomp) {
    goog.global['$jscomp'] = jscomp = {};
  }
  var transpile = jscomp.transpile;
  if (!transpile) {
    var transpilerPath = goog.basePath + goog.TRANSPILER;
    var transpilerCode = goog.loadFileSync_(transpilerPath);
    if (transpilerCode) {
      // This must be executed synchronously, since by the time we know we
      // need it, we're about to load and write the ES6 code synchronously,
      // so a normal script-tag load will be too slow. Wrapped in a function
      // so that code is eval'd in the global scope.
      (function() {
        eval(transpilerCode + '\n//# sourceURL=' + transpilerPath);
      }).call(goog.global);
      // Even though the transpiler is optional, if $gwtExport is found, it's
      // a sign the transpiler was loaded and the $jscomp.transpile *should*
      // be there.
      if (goog.global['$gwtExport'] && goog.global['$gwtExport']['$jscomp'] &&
          !goog.global['$gwtExport']['$jscomp']['transpile']) {
        throw new Error(
            'The transpiler did not properly export the "transpile" ' +
            'method. $gwtExport: ' + JSON.stringify(goog.global['$gwtExport']));
      }
      // transpile.js only exports a single $jscomp function, transpile. We
      // grab just that and add it to the existing definition of $jscomp which
      // contains the polyfills.
      goog.global['$jscomp'].transpile =
          goog.global['$gwtExport']['$jscomp']['transpile'];
      jscomp = goog.global['$jscomp'];
      transpile = jscomp.transpile;
    }
  }
  if (!transpile) {
    // The transpiler is an optional component.  If it's not available then
    // replace it with a pass-through function that simply logs.
    var suffix = ' requires transpilation but no transpiler was found.';
    transpile = jscomp.transpile = function(code, path) {
      // TODO(sdh): figure out some way to get this error to show up
      // in test results, noting that the failure may occur in many
      // different ways, including in loadModule() before the test
      // runner even comes up.
      goog.logToConsole_(path + suffix);
      return code;
    };
  }
  // Note: any transpilation errors/warnings will be logged to the console.
  return transpile(code, path, target);
};

//==============================================================================
// Language Enhancements
//==============================================================================


/**
 * This is a "fixed" version of the typeof operator.  It differs from the typeof
 * operator in such a way that null returns 'null' and arrays return 'array'.
 * @param {?} value The value to get the type of.
 * @return {string} The name of the type.
 */
goog.typeOf = function(value) {
  var s = typeof value;
  if (s == 'object') {
    if (value) {
      // Check these first, so we can avoid calling Object.prototype.toString if
      // possible.
      //
      // IE improperly marshals typeof across execution contexts, but a
      // cross-context object will still return false for "instanceof Object".
      if (value instanceof Array) {
        return 'array';
      } else if (value instanceof Object) {
        return s;
      }

      // HACK: In order to use an Object prototype method on the arbitrary
      //   value, the compiler requires the value be cast to type Object,
      //   even though the ECMA spec explicitly allows it.
      var className = Object.prototype.toString.call(
          /** @type {!Object} */ (value));
      // In Firefox 3.6, attempting to access iframe window objects' length
      // property throws an NS_ERROR_FAILURE, so we need to special-case it
      // here.
      if (className == '[object Window]') {
        return 'object';
      }

      // We cannot always use constructor == Array or instanceof Array because
      // different frames have different Array objects. In IE6, if the iframe
      // where the array was created is destroyed, the array loses its
      // prototype. Then dereferencing val.splice here throws an exception, so
      // we can't use goog.isFunction. Calling typeof directly returns 'unknown'
      // so that will work. In this case, this function will return false and
      // most array functions will still work because the array is still
      // array-like (supports length and []) even though it has lost its
      // prototype.
      // Mark Miller noticed that Object.prototype.toString
      // allows access to the unforgeable [[Class]] property.
      //  15.2.4.2 Object.prototype.toString ( )
      //  When the toString method is called, the following steps are taken:
      //      1. Get the [[Class]] property of this object.
      //      2. Compute a string value by concatenating the three strings
      //         "[object ", Result(1), and "]".
      //      3. Return Result(2).
      // and this behavior survives the destruction of the execution context.
      if ((className == '[object Array]' ||
           // In IE all non value types are wrapped as objects across window
           // boundaries (not iframe though) so we have to do object detection
           // for this edge case.
           typeof value.length == 'number' &&
               typeof value.splice != 'undefined' &&
               typeof value.propertyIsEnumerable != 'undefined' &&
               !value.propertyIsEnumerable('splice')

               )) {
        return 'array';
      }
      // HACK: There is still an array case that fails.
      //     function ArrayImpostor() {}
      //     ArrayImpostor.prototype = [];
      //     var impostor = new ArrayImpostor;
      // this can be fixed by getting rid of the fast path
      // (value instanceof Array) and solely relying on
      // (value && Object.prototype.toString.vall(value) === '[object Array]')
      // but that would require many more function calls and is not warranted
      // unless closure code is receiving objects from untrusted sources.

      // IE in cross-window calls does not correctly marshal the function type
      // (it appears just as an object) so we cannot use just typeof val ==
      // 'function'. However, if the object has a call property, it is a
      // function.
      if ((className == '[object Function]' ||
           typeof value.call != 'undefined' &&
               typeof value.propertyIsEnumerable != 'undefined' &&
               !value.propertyIsEnumerable('call'))) {
        return 'function';
      }

    } else {
      return 'null';
    }

  } else if (s == 'function' && typeof value.call == 'undefined') {
    // In Safari typeof nodeList returns 'function', and on Firefox typeof
    // behaves similarly for HTML{Applet,Embed,Object}, Elements and RegExps. We
    // would like to return object for those and we can detect an invalid
    // function by making sure that the function object has a call method.
    return 'object';
  }
  return s;
};


/**
 * Returns true if the specified value is null.
 * @param {?} val Variable to test.
 * @return {boolean} Whether variable is null.
 */
goog.isNull = function(val) {
  return val === null;
};


/**
 * Returns true if the specified value is defined and not null.
 * @param {?} val Variable to test.
 * @return {boolean} Whether variable is defined and not null.
 */
goog.isDefAndNotNull = function(val) {
  // Note that undefined == null.
  return val != null;
};


/**
 * Returns true if the specified value is an array.
 * @param {?} val Variable to test.
 * @return {boolean} Whether variable is an array.
 */
goog.isArray = function(val) {
  return goog.typeOf(val) == 'array';
};


/**
 * Returns true if the object looks like an array. To qualify as array like
 * the value needs to be either a NodeList or an object with a Number length
 * property. Note that for this function neither strings nor functions are
 * considered "array-like".
 *
 * @param {?} val Variable to test.
 * @return {boolean} Whether variable is an array.
 */
goog.isArrayLike = function(val) {
  var type = goog.typeOf(val);
  // We do not use goog.isObject here in order to exclude function values.
  return type == 'array' || type == 'object' && typeof val.length == 'number';
};


/**
 * Returns true if the object looks like a Date. To qualify as Date-like the
 * value needs to be an object and have a getFullYear() function.
 * @param {?} val Variable to test.
 * @return {boolean} Whether variable is a like a Date.
 */
goog.isDateLike = function(val) {
  return goog.isObject(val) && typeof val.getFullYear == 'function';
};


/**
 * Returns true if the specified value is a function.
 * @param {?} val Variable to test.
 * @return {boolean} Whether variable is a function.
 */
goog.isFunction = function(val) {
  return goog.typeOf(val) == 'function';
};


/**
 * Returns true if the specified value is an object.  This includes arrays and
 * functions.
 * @param {?} val Variable to test.
 * @return {boolean} Whether variable is an object.
 */
goog.isObject = function(val) {
  var type = typeof val;
  return type == 'object' && val != null || type == 'function';
  // return Object(val) === val also works, but is slower, especially if val is
  // not an object.
};


/**
 * Gets a unique ID for an object. This mutates the object so that further calls
 * with the same object as a parameter returns the same value. The unique ID is
 * guaranteed to be unique across the current session amongst objects that are
 * passed into `getUid`. There is no guarantee that the ID is unique or
 * consistent across sessions. It is unsafe to generate unique ID for function
 * prototypes.
 *
 * @param {Object} obj The object to get the unique ID for.
 * @return {number} The unique ID for the object.
 */
goog.getUid = function(obj) {
  // TODO(arv): Make the type stricter, do not accept null.

  // In Opera window.hasOwnProperty exists but always returns false so we avoid
  // using it. As a consequence the unique ID generated for BaseClass.prototype
  // and SubClass.prototype will be the same.
  return obj[goog.UID_PROPERTY_] ||
      (obj[goog.UID_PROPERTY_] = ++goog.uidCounter_);
};


/**
 * Whether the given object is already assigned a unique ID.
 *
 * This does not modify the object.
 *
 * @param {!Object} obj The object to check.
 * @return {boolean} Whether there is an assigned unique id for the object.
 */
goog.hasUid = function(obj) {
  return !!obj[goog.UID_PROPERTY_];
};


/**
 * Removes the unique ID from an object. This is useful if the object was
 * previously mutated using `goog.getUid` in which case the mutation is
 * undone.
 * @param {Object} obj The object to remove the unique ID field from.
 */
goog.removeUid = function(obj) {
  // TODO(arv): Make the type stricter, do not accept null.

  // In IE, DOM nodes are not instances of Object and throw an exception if we
  // try to delete.  Instead we try to use removeAttribute.
  if (obj !== null && 'removeAttribute' in obj) {
    obj.removeAttribute(goog.UID_PROPERTY_);
  }

  try {
    delete obj[goog.UID_PROPERTY_];
  } catch (ex) {
  }
};


/**
 * Name for unique ID property. Initialized in a way to help avoid collisions
 * with other closure JavaScript on the same page.
 * @type {string}
 * @private
 */
goog.UID_PROPERTY_ = 'closure_uid_' + ((Math.random() * 1e9) >>> 0);


/**
 * Counter for UID.
 * @type {number}
 * @private
 */
goog.uidCounter_ = 0;


/**
 * Adds a hash code field to an object. The hash code is unique for the
 * given object.
 * @param {Object} obj The object to get the hash code for.
 * @return {number} The hash code for the object.
 * @deprecated Use goog.getUid instead.
 */
goog.getHashCode = goog.getUid;


/**
 * Removes the hash code field from an object.
 * @param {Object} obj The object to remove the field from.
 * @deprecated Use goog.removeUid instead.
 */
goog.removeHashCode = goog.removeUid;


/**
 * Clones a value. The input may be an Object, Array, or basic type. Objects and
 * arrays will be cloned recursively.
 *
 * WARNINGS:
 * <code>goog.cloneObject</code> does not detect reference loops. Objects that
 * refer to themselves will cause infinite recursion.
 *
 * <code>goog.cloneObject</code> is unaware of unique identifiers, and copies
 * UIDs created by <code>getUid</code> into cloned results.
 *
 * @param {*} obj The value to clone.
 * @return {*} A clone of the input value.
 * @deprecated goog.cloneObject is unsafe. Prefer the goog.object methods.
 */
goog.cloneObject = function(obj) {
  var type = goog.typeOf(obj);
  if (type == 'object' || type == 'array') {
    if (typeof obj.clone === 'function') {
      return obj.clone();
    }
    var clone = type == 'array' ? [] : {};
    for (var key in obj) {
      clone[key] = goog.cloneObject(obj[key]);
    }
    return clone;
  }

  return obj;
};


/**
 * A native implementation of goog.bind.
 * @param {?function(this:T, ...)} fn A function to partially apply.
 * @param {T} selfObj Specifies the object which this should point to when the
 *     function is run.
 * @param {...*} var_args Additional arguments that are partially applied to the
 *     function.
 * @return {!Function} A partially-applied form of the function goog.bind() was
 *     invoked as a method of.
 * @template T
 * @private
 */
goog.bindNative_ = function(fn, selfObj, var_args) {
  return /** @type {!Function} */ (fn.call.apply(fn.bind, arguments));
};


/**
 * A pure-JS implementation of goog.bind.
 * @param {?function(this:T, ...)} fn A function to partially apply.
 * @param {T} selfObj Specifies the object which this should point to when the
 *     function is run.
 * @param {...*} var_args Additional arguments that are partially applied to the
 *     function.
 * @return {!Function} A partially-applied form of the function goog.bind() was
 *     invoked as a method of.
 * @template T
 * @private
 */
goog.bindJs_ = function(fn, selfObj, var_args) {
  if (!fn) {
    throw new Error();
  }

  if (arguments.length > 2) {
    var boundArgs = Array.prototype.slice.call(arguments, 2);
    return function() {
      // Prepend the bound arguments to the current arguments.
      var newArgs = Array.prototype.slice.call(arguments);
      Array.prototype.unshift.apply(newArgs, boundArgs);
      return fn.apply(selfObj, newArgs);
    };

  } else {
    return function() {
      return fn.apply(selfObj, arguments);
    };
  }
};


/**
 * Partially applies this function to a particular 'this object' and zero or
 * more arguments. The result is a new function with some arguments of the first
 * function pre-filled and the value of this 'pre-specified'.
 *
 * Remaining arguments specified at call-time are appended to the pre-specified
 * ones.
 *
 * Also see: {@link #partial}.
 *
 * Usage:
 * <pre>var barMethBound = goog.bind(myFunction, myObj, 'arg1', 'arg2');
 * barMethBound('arg3', 'arg4');</pre>
 *
 * @param {?function(this:T, ...)} fn A function to partially apply.
 * @param {T} selfObj Specifies the object which this should point to when the
 *     function is run.
 * @param {...*} var_args Additional arguments that are partially applied to the
 *     function.
 * @return {!Function} A partially-applied form of the function goog.bind() was
 *     invoked as a method of.
 * @template T
 * @suppress {deprecated} See above.
 */
goog.bind = function(fn, selfObj, var_args) {
  // TODO(nicksantos): narrow the type signature.
  if (Function.prototype.bind &&
      // NOTE(nicksantos): Somebody pulled base.js into the default Chrome
      // extension environment. This means that for Chrome extensions, they get
      // the implementation of Function.prototype.bind that calls goog.bind
      // instead of the native one. Even worse, we don't want to introduce a
      // circular dependency between goog.bind and Function.prototype.bind, so
      // we have to hack this to make sure it works correctly.
      Function.prototype.bind.toString().indexOf('native code') != -1) {
    goog.bind = goog.bindNative_;
  } else {
    goog.bind = goog.bindJs_;
  }
  return goog.bind.apply(null, arguments);
};


/**
 * Like goog.bind(), except that a 'this object' is not required. Useful when
 * the target function is already bound.
 *
 * Usage:
 * var g = goog.partial(f, arg1, arg2);
 * g(arg3, arg4);
 *
 * @param {Function} fn A function to partially apply.
 * @param {...*} var_args Additional arguments that are partially applied to fn.
 * @return {!Function} A partially-applied form of the function goog.partial()
 *     was invoked as a method of.
 */
goog.partial = function(fn, var_args) {
  var args = Array.prototype.slice.call(arguments, 1);
  return function() {
    // Clone the array (with slice()) and append additional arguments
    // to the existing arguments.
    var newArgs = args.slice();
    newArgs.push.apply(newArgs, arguments);
    return fn.apply(/** @type {?} */ (this), newArgs);
  };
};


/**
 * Copies all the members of a source object to a target object. This method
 * does not work on all browsers for all objects that contain keys such as
 * toString or hasOwnProperty. Use goog.object.extend for this purpose.
 * @param {Object} target Target.
 * @param {Object} source Source.
 */
goog.mixin = function(target, source) {
  for (var x in source) {
    target[x] = source[x];
  }

  // For IE7 or lower, the for-in-loop does not contain any properties that are
  // not enumerable on the prototype object (for example, isPrototypeOf from
  // Object.prototype) but also it will not include 'replace' on objects that
  // extend String and change 'replace' (not that it is common for anyone to
  // extend anything except Object).
};


/**
 * @return {number} An integer value representing the number of milliseconds
 *     between midnight, January 1, 1970 and the current time.
 */
goog.now = (goog.TRUSTED_SITE && Date.now) || (function() {
             // Unary plus operator converts its operand to a number which in
             // the case of
             // a date is done by calling getTime().
             return +new Date();
           });


/**
 * Evals JavaScript in the global scope.  In IE this uses execScript, other
 * browsers use goog.global.eval. If goog.global.eval does not evaluate in the
 * global scope (for example, in Safari), appends a script tag instead.
 * Throws an exception if neither execScript or eval is defined.
 * @param {string} script JavaScript string.
 */
goog.globalEval = function(script) {
  if (goog.global.execScript) {
    goog.global.execScript(script, 'JavaScript');
  } else if (goog.global.eval) {
    // Test to see if eval works
    if (goog.evalWorksForGlobals_ == null) {
      try {
        goog.global.eval('var _evalTest_ = 1;');
      } catch (ignore) {
      }
      if (typeof goog.global['_evalTest_'] != 'undefined') {
        try {
          delete goog.global['_evalTest_'];
        } catch (ignore) {
          // Microsoft edge fails the deletion above in strict mode.
        }
        goog.evalWorksForGlobals_ = true;
      } else {
        goog.evalWorksForGlobals_ = false;
      }
    }

    if (goog.evalWorksForGlobals_) {
      goog.global.eval(script);
    } else {
      /** @type {!Document} */
      var doc = goog.global.document;
      var scriptElt =
          /** @type {!HTMLScriptElement} */ (doc.createElement('SCRIPT'));
      scriptElt.type = 'text/javascript';
      scriptElt.defer = false;
      // Note(user): can't use .innerHTML since "t('<test>')" will fail and
      // .text doesn't work in Safari 2.  Therefore we append a text node.
      scriptElt.appendChild(doc.createTextNode(script));
      doc.head.appendChild(scriptElt);
      doc.head.removeChild(scriptElt);
    }
  } else {
    throw new Error('goog.globalEval not available');
  }
};


/**
 * Indicates whether or not we can call 'eval' directly to eval code in the
 * global scope. Set to a Boolean by the first call to goog.globalEval (which
 * empirically tests whether eval works for globals). @see goog.globalEval
 * @type {?boolean}
 * @private
 */
goog.evalWorksForGlobals_ = null;


/**
 * Optional map of CSS class names to obfuscated names used with
 * goog.getCssName().
 * @private {!Object<string, string>|undefined}
 * @see goog.setCssNameMapping
 */
goog.cssNameMapping_;


/**
 * Optional obfuscation style for CSS class names. Should be set to either
 * 'BY_WHOLE' or 'BY_PART' if defined.
 * @type {string|undefined}
 * @private
 * @see goog.setCssNameMapping
 */
goog.cssNameMappingStyle_;



/**
 * A hook for modifying the default behavior goog.getCssName. The function
 * if present, will receive the standard output of the goog.getCssName as
 * its input.
 *
 * @type {(function(string):string)|undefined}
 */
goog.global.CLOSURE_CSS_NAME_MAP_FN;


/**
 * Handles strings that are intended to be used as CSS class names.
 *
 * This function works in tandem with @see goog.setCssNameMapping.
 *
 * Without any mapping set, the arguments are simple joined with a hyphen and
 * passed through unaltered.
 *
 * When there is a mapping, there are two possible styles in which these
 * mappings are used. In the BY_PART style, each part (i.e. in between hyphens)
 * of the passed in css name is rewritten according to the map. In the BY_WHOLE
 * style, the full css name is looked up in the map directly. If a rewrite is
 * not specified by the map, the compiler will output a warning.
 *
 * When the mapping is passed to the compiler, it will replace calls to
 * goog.getCssName with the strings from the mapping, e.g.
 *     var x = goog.getCssName('foo');
 *     var y = goog.getCssName(this.baseClass, 'active');
 *  becomes:
 *     var x = 'foo';
 *     var y = this.baseClass + '-active';
 *
 * If one argument is passed it will be processed, if two are passed only the
 * modifier will be processed, as it is assumed the first argument was generated
 * as a result of calling goog.getCssName.
 *
 * @param {string} className The class name.
 * @param {string=} opt_modifier A modifier to be appended to the class name.
 * @return {string} The class name or the concatenation of the class name and
 *     the modifier.
 */
goog.getCssName = function(className, opt_modifier) {
  // String() is used for compatibility with compiled soy where the passed
  // className can be non-string objects.
  if (String(className).charAt(0) == '.') {
    throw new Error(
        'className passed in goog.getCssName must not start with ".".' +
        ' You passed: ' + className);
  }

  var getMapping = function(cssName) {
    return goog.cssNameMapping_[cssName] || cssName;
  };

  var renameByParts = function(cssName) {
    // Remap all the parts individually.
    var parts = cssName.split('-');
    var mapped = [];
    for (var i = 0; i < parts.length; i++) {
      mapped.push(getMapping(parts[i]));
    }
    return mapped.join('-');
  };

  var rename;
  if (goog.cssNameMapping_) {
    rename =
        goog.cssNameMappingStyle_ == 'BY_WHOLE' ? getMapping : renameByParts;
  } else {
    rename = function(a) {
      return a;
    };
  }

  var result =
      opt_modifier ? className + '-' + rename(opt_modifier) : rename(className);

  // The special CLOSURE_CSS_NAME_MAP_FN allows users to specify further
  // processing of the class name.
  if (goog.global.CLOSURE_CSS_NAME_MAP_FN) {
    return goog.global.CLOSURE_CSS_NAME_MAP_FN(result);
  }

  return result;
};


/**
 * Sets the map to check when returning a value from goog.getCssName(). Example:
 * <pre>
 * goog.setCssNameMapping({
 *   "goog": "a",
 *   "disabled": "b",
 * });
 *
 * var x = goog.getCssName('goog');
 * // The following evaluates to: "a a-b".
 * goog.getCssName('goog') + ' ' + goog.getCssName(x, 'disabled')
 * </pre>
 * When declared as a map of string literals to string literals, the JSCompiler
 * will replace all calls to goog.getCssName() using the supplied map if the
 * --process_closure_primitives flag is set.
 *
 * @param {!Object} mapping A map of strings to strings where keys are possible
 *     arguments to goog.getCssName() and values are the corresponding values
 *     that should be returned.
 * @param {string=} opt_style The style of css name mapping. There are two valid
 *     options: 'BY_PART', and 'BY_WHOLE'.
 * @see goog.getCssName for a description.
 */
goog.setCssNameMapping = function(mapping, opt_style) {
  goog.cssNameMapping_ = mapping;
  goog.cssNameMappingStyle_ = opt_style;
};


/**
 * To use CSS renaming in compiled mode, one of the input files should have a
 * call to goog.setCssNameMapping() with an object literal that the JSCompiler
 * can extract and use to replace all calls to goog.getCssName(). In uncompiled
 * mode, JavaScript code should be loaded before this base.js file that declares
 * a global variable, CLOSURE_CSS_NAME_MAPPING, which is used below. This is
 * to ensure that the mapping is loaded before any calls to goog.getCssName()
 * are made in uncompiled mode.
 *
 * A hook for overriding the CSS name mapping.
 * @type {!Object<string, string>|undefined}
 */
goog.global.CLOSURE_CSS_NAME_MAPPING;


if (!COMPILED && goog.global.CLOSURE_CSS_NAME_MAPPING) {
  // This does not call goog.setCssNameMapping() because the JSCompiler
  // requires that goog.setCssNameMapping() be called with an object literal.
  goog.cssNameMapping_ = goog.global.CLOSURE_CSS_NAME_MAPPING;
}


/**
 * Gets a localized message.
 *
 * This function is a compiler primitive. If you give the compiler a localized
 * message bundle, it will replace the string at compile-time with a localized
 * version, and expand goog.getMsg call to a concatenated string.
 *
 * Messages must be initialized in the form:
 * <code>
 * var MSG_NAME = goog.getMsg('Hello {$placeholder}', {'placeholder': 'world'});
 * </code>
 *
 * This function produces a string which should be treated as plain text. Use
 * {@link goog.html.SafeHtmlFormatter} in conjunction with goog.getMsg to
 * produce SafeHtml.
 *
 * @param {string} str Translatable string, places holders in the form {$foo}.
 * @param {Object<string, string>=} opt_values Maps place holder name to value.
 * @return {string} message with placeholders filled.
 */
goog.getMsg = function(str, opt_values) {
  if (opt_values) {
    str = str.replace(/\{\$([^}]+)}/g, function(match, key) {
      return (opt_values != null && key in opt_values) ? opt_values[key] :
                                                         match;
    });
  }
  return str;
};


/**
 * Gets a localized message. If the message does not have a translation, gives a
 * fallback message.
 *
 * This is useful when introducing a new message that has not yet been
 * translated into all languages.
 *
 * This function is a compiler primitive. Must be used in the form:
 * <code>var x = goog.getMsgWithFallback(MSG_A, MSG_B);</code>
 * where MSG_A and MSG_B were initialized with goog.getMsg.
 *
 * @param {string} a The preferred message.
 * @param {string} b The fallback message.
 * @return {string} The best translated message.
 */
goog.getMsgWithFallback = function(a, b) {
  return a;
};


/**
 * Exposes an unobfuscated global namespace path for the given object.
 * Note that fields of the exported object *will* be obfuscated, unless they are
 * exported in turn via this function or goog.exportProperty.
 *
 * Also handy for making public items that are defined in anonymous closures.
 *
 * ex. goog.exportSymbol('public.path.Foo', Foo);
 *
 * ex. goog.exportSymbol('public.path.Foo.staticFunction', Foo.staticFunction);
 *     public.path.Foo.staticFunction();
 *
 * ex. goog.exportSymbol('public.path.Foo.prototype.myMethod',
 *                       Foo.prototype.myMethod);
 *     new public.path.Foo().myMethod();
 *
 * @param {string} publicPath Unobfuscated name to export.
 * @param {*} object Object the name should point to.
 * @param {Object=} opt_objectToExportTo The object to add the path to; default
 *     is goog.global.
 */
goog.exportSymbol = function(publicPath, object, opt_objectToExportTo) {
  goog.exportPath_(publicPath, object, opt_objectToExportTo);
};


/**
 * Exports a property unobfuscated into the object's namespace.
 * ex. goog.exportProperty(Foo, 'staticFunction', Foo.staticFunction);
 * ex. goog.exportProperty(Foo.prototype, 'myMethod', Foo.prototype.myMethod);
 * @param {Object} object Object whose static property is being exported.
 * @param {string} publicName Unobfuscated name to export.
 * @param {*} symbol Object the name should point to.
 */
goog.exportProperty = function(object, publicName, symbol) {
  object[publicName] = symbol;
};


/**
 * Inherit the prototype methods from one constructor into another.
 *
 * Usage:
 * <pre>
 * function ParentClass(a, b) { }
 * ParentClass.prototype.foo = function(a) { };
 *
 * function ChildClass(a, b, c) {
 *   ChildClass.base(this, 'constructor', a, b);
 * }
 * goog.inherits(ChildClass, ParentClass);
 *
 * var child = new ChildClass('a', 'b', 'see');
 * child.foo(); // This works.
 * </pre>
 *
 * @param {!Function} childCtor Child class.
 * @param {!Function} parentCtor Parent class.
 * @suppress {strictMissingProperties} superClass_ and base is not defined on
 *    Function.
 */
goog.inherits = function(childCtor, parentCtor) {
  /** @constructor */
  function tempCtor() {}
  tempCtor.prototype = parentCtor.prototype;
  childCtor.superClass_ = parentCtor.prototype;
  childCtor.prototype = new tempCtor();
  /** @override */
  childCtor.prototype.constructor = childCtor;

  /**
   * Calls superclass constructor/method.
   *
   * This function is only available if you use goog.inherits to
   * express inheritance relationships between classes.
   *
   * NOTE: This is a replacement for goog.base and for superClass_
   * property defined in childCtor.
   *
   * @param {!Object} me Should always be "this".
   * @param {string} methodName The method name to call. Calling
   *     superclass constructor can be done with the special string
   *     'constructor'.
   * @param {...*} var_args The arguments to pass to superclass
   *     method/constructor.
   * @return {*} The return value of the superclass method/constructor.
   */
  childCtor.base = function(me, methodName, var_args) {
    // Copying using loop to avoid deop due to passing arguments object to
    // function. This is faster in many JS engines as of late 2014.
    var args = new Array(arguments.length - 2);
    for (var i = 2; i < arguments.length; i++) {
      args[i - 2] = arguments[i];
    }
    return parentCtor.prototype[methodName].apply(me, args);
  };
};


/**
 * Call up to the superclass.
 *
 * If this is called from a constructor, then this calls the superclass
 * constructor with arguments 1-N.
 *
 * If this is called from a prototype method, then you must pass the name of the
 * method as the second argument to this function. If you do not, you will get a
 * runtime error. This calls the superclass' method with arguments 2-N.
 *
 * This function only works if you use goog.inherits to express inheritance
 * relationships between your classes.
 *
 * This function is a compiler primitive. At compile-time, the compiler will do
 * macro expansion to remove a lot of the extra overhead that this function
 * introduces. The compiler will also enforce a lot of the assumptions that this
 * function makes, and treat it as a compiler error if you break them.
 *
 * @param {!Object} me Should always be "this".
 * @param {*=} opt_methodName The method name if calling a super method.
 * @param {...*} var_args The rest of the arguments.
 * @return {*} The return value of the superclass method.
 * @suppress {es5Strict} This method can not be used in strict mode, but
 *     all Closure Library consumers must depend on this file.
 * @deprecated goog.base is not strict mode compatible.  Prefer the static
 *     "base" method added to the constructor by goog.inherits
 *     or ES6 classes and the "super" keyword.
 */
goog.base = function(me, opt_methodName, var_args) {
  var caller = arguments.callee.caller;

  if (goog.STRICT_MODE_COMPATIBLE || (goog.DEBUG && !caller)) {
    throw new Error(
        'arguments.caller not defined.  goog.base() cannot be used ' +
        'with strict mode code. See ' +
        'http://www.ecma-international.org/ecma-262/5.1/#sec-C');
  }

  if (typeof caller.superClass_ !== 'undefined') {
    // Copying using loop to avoid deop due to passing arguments object to
    // function. This is faster in many JS engines as of late 2014.
    var ctorArgs = new Array(arguments.length - 1);
    for (var i = 1; i < arguments.length; i++) {
      ctorArgs[i - 1] = arguments[i];
    }
    // This is a constructor. Call the superclass constructor.
    return /** @type {!Function} */ (caller.superClass_)
        .constructor.apply(me, ctorArgs);
  }

  if (typeof opt_methodName != 'string' && typeof opt_methodName != 'symbol') {
    throw new Error(
        'method names provided to goog.base must be a string or a symbol');
  }

  // Copying using loop to avoid deop due to passing arguments object to
  // function. This is faster in many JS engines as of late 2014.
  var args = new Array(arguments.length - 2);
  for (var i = 2; i < arguments.length; i++) {
    args[i - 2] = arguments[i];
  }
  var foundCaller = false;
  for (var ctor = me.constructor; ctor;
       ctor = ctor.superClass_ && ctor.superClass_.constructor) {
    if (ctor.prototype[opt_methodName] === caller) {
      foundCaller = true;
    } else if (foundCaller) {
      return ctor.prototype[opt_methodName].apply(me, args);
    }
  }

  // If we did not find the caller in the prototype chain, then one of two
  // things happened:
  // 1) The caller is an instance method.
  // 2) This method was not called by the right caller.
  if (me[opt_methodName] === caller) {
    return me.constructor.prototype[opt_methodName].apply(me, args);
  } else {
    throw new Error(
        'goog.base called from a method of one name ' +
        'to a method of a different name');
  }
};


/**
 * Allow for aliasing within scope functions.  This function exists for
 * uncompiled code - in compiled code the calls will be inlined and the aliases
 * applied.  In uncompiled code the function is simply run since the aliases as
 * written are valid JavaScript.
 *
 *
 * @param {function()} fn Function to call.  This function can contain aliases
 *     to namespaces (e.g. "var dom = goog.dom") or classes
 *     (e.g. "var Timer = goog.Timer").
 */
goog.scope = function(fn) {
  if (goog.isInModuleLoader_()) {
    throw new Error('goog.scope is not supported within a module.');
  }
  fn.call(goog.global);
};


/*
 * To support uncompiled, strict mode bundles that use eval to divide source
 * like so:
 *    eval('someSource;//# sourceUrl sourcefile.js');
 * We need to export the globally defined symbols "goog" and "COMPILED".
 * Exporting "goog" breaks the compiler optimizations, so we required that
 * be defined externally.
 * NOTE: We don't use goog.exportSymbol here because we don't want to trigger
 * extern generation when that compiler option is enabled.
 */
if (!COMPILED) {
  goog.global['COMPILED'] = COMPILED;
}


//==============================================================================
// goog.defineClass implementation
//==============================================================================


/**
 * Creates a restricted form of a Closure "class":
 *   - from the compiler's perspective, the instance returned from the
 *     constructor is sealed (no new properties may be added).  This enables
 *     better checks.
 *   - the compiler will rewrite this definition to a form that is optimal
 *     for type checking and optimization (initially this will be a more
 *     traditional form).
 *
 * @param {Function} superClass The superclass, Object or null.
 * @param {goog.defineClass.ClassDescriptor} def
 *     An object literal describing
 *     the class.  It may have the following properties:
 *     "constructor": the constructor function
 *     "statics": an object literal containing methods to add to the constructor
 *        as "static" methods or a function that will receive the constructor
 *        function as its only parameter to which static properties can
 *        be added.
 *     all other properties are added to the prototype.
 * @return {!Function} The class constructor.
 */
goog.defineClass = function(superClass, def) {
  // TODO(johnlenz): consider making the superClass an optional parameter.
  var constructor = def.constructor;
  var statics = def.statics;
  // Wrap the constructor prior to setting up the prototype and static methods.
  if (!constructor || constructor == Object.prototype.constructor) {
    constructor = function() {
      throw new Error(
          'cannot instantiate an interface (no constructor defined).');
    };
  }

  var cls = goog.defineClass.createSealingConstructor_(constructor, superClass);
  if (superClass) {
    goog.inherits(cls, superClass);
  }

  // Remove all the properties that should not be copied to the prototype.
  delete def.constructor;
  delete def.statics;

  goog.defineClass.applyProperties_(cls.prototype, def);
  if (statics != null) {
    if (statics instanceof Function) {
      statics(cls);
    } else {
      goog.defineClass.applyProperties_(cls, statics);
    }
  }

  return cls;
};


/**
 * @typedef {{
 *   constructor: (!Function|undefined),
 *   statics: (Object|undefined|function(Function):void)
 * }}
 */
goog.defineClass.ClassDescriptor;


/**
 * @define {boolean} Whether the instances returned by goog.defineClass should
 *     be sealed when possible.
 *
 * When sealing is disabled the constructor function will not be wrapped by
 * goog.defineClass, making it incompatible with ES6 class methods.
 */
goog.define('goog.defineClass.SEAL_CLASS_INSTANCES', goog.DEBUG);


/**
 * If goog.defineClass.SEAL_CLASS_INSTANCES is enabled and Object.seal is
 * defined, this function will wrap the constructor in a function that seals the
 * results of the provided constructor function.
 *
 * @param {!Function} ctr The constructor whose results maybe be sealed.
 * @param {Function} superClass The superclass constructor.
 * @return {!Function} The replacement constructor.
 * @private
 */
goog.defineClass.createSealingConstructor_ = function(ctr, superClass) {
  if (!goog.defineClass.SEAL_CLASS_INSTANCES) {
    // Do now wrap the constructor when sealing is disabled. Angular code
    // depends on this for injection to work properly.
    return ctr;
  }

  // Compute whether the constructor is sealable at definition time, rather
  // than when the instance is being constructed.
  var superclassSealable = !goog.defineClass.isUnsealable_(superClass);

  /**
   * @this {Object}
   * @return {?}
   */
  var wrappedCtr = function() {
    // Don't seal an instance of a subclass when it calls the constructor of
    // its super class as there is most likely still setup to do.
    var instance = ctr.apply(this, arguments) || this;
    instance[goog.UID_PROPERTY_] = instance[goog.UID_PROPERTY_];

    if (this.constructor === wrappedCtr && superclassSealable &&
        Object.seal instanceof Function) {
      Object.seal(instance);
    }
    return instance;
  };

  return wrappedCtr;
};


/**
 * @param {Function} ctr The constructor to test.
 * @return {boolean} Whether the constructor has been tagged as unsealable
 *     using goog.tagUnsealableClass.
 * @private
 */
goog.defineClass.isUnsealable_ = function(ctr) {
  return ctr && ctr.prototype &&
      ctr.prototype[goog.UNSEALABLE_CONSTRUCTOR_PROPERTY_];
};


// TODO(johnlenz): share these values with the goog.object
/**
 * The names of the fields that are defined on Object.prototype.
 * @type {!Array<string>}
 * @private
 * @const
 */
goog.defineClass.OBJECT_PROTOTYPE_FIELDS_ = [
  'constructor', 'hasOwnProperty', 'isPrototypeOf', 'propertyIsEnumerable',
  'toLocaleString', 'toString', 'valueOf'
];


// TODO(johnlenz): share this function with the goog.object
/**
 * @param {!Object} target The object to add properties to.
 * @param {!Object} source The object to copy properties from.
 * @private
 */
goog.defineClass.applyProperties_ = function(target, source) {
  // TODO(johnlenz): update this to support ES5 getters/setters

  var key;
  for (key in source) {
    if (Object.prototype.hasOwnProperty.call(source, key)) {
      target[key] = source[key];
    }
  }

  // For IE the for-in-loop does not contain any properties that are not
  // enumerable on the prototype object (for example isPrototypeOf from
  // Object.prototype) and it will also not include 'replace' on objects that
  // extend String and change 'replace' (not that it is common for anyone to
  // extend anything except Object).
  for (var i = 0; i < goog.defineClass.OBJECT_PROTOTYPE_FIELDS_.length; i++) {
    key = goog.defineClass.OBJECT_PROTOTYPE_FIELDS_[i];
    if (Object.prototype.hasOwnProperty.call(source, key)) {
      target[key] = source[key];
    }
  }
};


/**
 * Sealing classes breaks the older idiom of assigning properties on the
 * prototype rather than in the constructor. As such, goog.defineClass
 * must not seal subclasses of these old-style classes until they are fixed.
 * Until then, this marks a class as "broken", instructing defineClass
 * not to seal subclasses.
 * @param {!Function} ctr The legacy constructor to tag as unsealable.
 */
goog.tagUnsealableClass = function(ctr) {
  if (!COMPILED && goog.defineClass.SEAL_CLASS_INSTANCES) {
    ctr.prototype[goog.UNSEALABLE_CONSTRUCTOR_PROPERTY_] = true;
  }
};


/**
 * Name for unsealable tag property.
 * @const @private {string}
 */
goog.UNSEALABLE_CONSTRUCTOR_PROPERTY_ = 'goog_defineClass_legacy_unsealable';


// There's a bug in the compiler where without collapse properties the
// Closure namespace defines do not guard code correctly. To help reduce code
// size also check for !COMPILED even though it redundant until this is fixed.
if (!COMPILED && goog.DEPENDENCIES_ENABLED) {

  /**
   * Tries to detect whether is in the context of an HTML document.
   * @return {boolean} True if it looks like HTML document.
   * @private
   */
  goog.inHtmlDocument_ = function() {
    /** @type {!Document} */
    var doc = goog.global.document;
    return doc != null && 'write' in doc;  // XULDocument misses write.
  };


  /**
   * We'd like to check for if the document readyState is 'loading'; however
   * there are bugs on IE 10 and below where the readyState being anything other
   * than 'complete' is not reliable.
   * @return {boolean}
   * @private
   */
  goog.isDocumentLoading_ = function() {
    // attachEvent is available on IE 6 thru 10 only, and thus can be used to
    // detect those browsers.
    /** @type {!HTMLDocument} */
    var doc = goog.global.document;
    return doc.attachEvent ? doc.readyState != 'complete' :
                             doc.readyState == 'loading';
  };


  /**
   * Tries to detect the base path of base.js script that bootstraps Closure.
   * @private
   */
  goog.findBasePath_ = function() {
    if (goog.isDef(goog.global.CLOSURE_BASE_PATH) &&
        // Anti DOM-clobbering runtime check (b/37736576).
        goog.isString(goog.global.CLOSURE_BASE_PATH)) {
      goog.basePath = goog.global.CLOSURE_BASE_PATH;
      return;
    } else if (!goog.inHtmlDocument_()) {
      return;
    }
    /** @type {!Document} */
    var doc = goog.global.document;
    // If we have a currentScript available, use it exclusively.
    var currentScript = doc.currentScript;
    if (currentScript) {
      var scripts = [currentScript];
    } else {
      var scripts = doc.getElementsByTagName('SCRIPT');
    }
    // Search backwards since the current script is in almost all cases the one
    // that has base.js.
    for (var i = scripts.length - 1; i >= 0; --i) {
      var script = /** @type {!HTMLScriptElement} */ (scripts[i]);
      var src = script.src;
      var qmark = src.lastIndexOf('?');
      var l = qmark == -1 ? src.length : qmark;
      if (src.substr(l - 7, 7) == 'base.js') {
        goog.basePath = src.substr(0, l - 7);
        return;
      }
    }
  };

  goog.findBasePath_();

  /** @struct @constructor @final */
  goog.Transpiler = function() {
    /** @private {?Object<string, boolean>} */
    this.requiresTranspilation_ = null;
    /** @private {string} */
    this.transpilationTarget_ = goog.TRANSPILE_TO_LANGUAGE;
  };


  /**
   * Returns a newly created map from language mode string to a boolean
   * indicating whether transpilation should be done for that mode as well as
   * the highest level language that this environment supports.
   *
   * Guaranteed invariant:
   * For any two modes, l1 and l2 where l2 is a newer mode than l1,
   * `map[l1] == true` implies that `map[l2] == true`.
   *
   * Note this method is extracted and used elsewhere, so it cannot rely on
   * anything external (it should easily be able to be transformed into a
   * standalone, top level function).
   *
   * @private
   * @return {{
   *   target: string,
   *   map: !Object<string, boolean>
   * }}
   */
  goog.Transpiler.prototype.createRequiresTranspilation_ = function() {
    var transpilationTarget = 'es3';
    var /** !Object<string, boolean> */ requiresTranspilation = {'es3': false};
    var transpilationRequiredForAllLaterModes = false;

    /**
     * Adds an entry to requiresTranspliation for the given language mode.
     *
     * IMPORTANT: Calls must be made in order from oldest to newest language
     * mode.
     * @param {string} modeName
     * @param {function(): boolean} isSupported Returns true if the JS engine
     *     supports the given mode.
     */
    function addNewerLanguageTranspilationCheck(modeName, isSupported) {
      if (transpilationRequiredForAllLaterModes) {
        requiresTranspilation[modeName] = true;
      } else if (isSupported()) {
        transpilationTarget = modeName;
        requiresTranspilation[modeName] = false;
      } else {
        requiresTranspilation[modeName] = true;
        transpilationRequiredForAllLaterModes = true;
      }
    }

    /**
     * Does the given code evaluate without syntax errors and return a truthy
     * result?
     */
    function /** boolean */ evalCheck(/** string */ code) {
      try {
        return !!eval(code);
      } catch (ignored) {
        return false;
      }
    }

    var userAgent = goog.global.navigator && goog.global.navigator.userAgent ?
        goog.global.navigator.userAgent :
        '';

    // Identify ES3-only browsers by their incorrect treatment of commas.
    addNewerLanguageTranspilationCheck('es5', function() {
      return evalCheck('[1,].length==1');
    });
    addNewerLanguageTranspilationCheck('es6', function() {
      // Edge has a non-deterministic (i.e., not reproducible) bug with ES6:
      // https://github.com/Microsoft/ChakraCore/issues/1496.
      var re = /Edge\/(\d+)(\.\d)*/i;
      var edgeUserAgent = userAgent.match(re);
      if (edgeUserAgent && Number(edgeUserAgent[1]) < 15) {
        return false;
      }
      // Test es6: [FF50 (?), Edge 14 (?), Chrome 50]
      //   (a) default params (specifically shadowing locals),
      //   (b) destructuring, (c) block-scoped functions,
      //   (d) for-of (const), (e) new.target/Reflect.construct
      var es6fullTest =
          'class X{constructor(){if(new.target!=String)throw 1;this.x=42}}' +
          'let q=Reflect.construct(X,[],String);if(q.x!=42||!(q instanceof ' +
          'String))throw 1;for(const a of[2,3]){if(a==2)continue;function ' +
          'f(z={a}){let a=0;return z.a}{function f(){return 0;}}return f()' +
          '==3}';

      return evalCheck('(()=>{"use strict";' + es6fullTest + '})()');
    });
    // TODO(joeltine): Remove es6-impl references for b/31340605.
    // Consider es6-impl (widely-implemented es6 features) to be supported
    // whenever es6 is supported. Technically es6-impl is a lower level of
    // support than es6, but we don't have tests specifically for it.
    addNewerLanguageTranspilationCheck('es6-impl', function() {
      return true;
    });
    // ** and **= are the only new features in 'es7'
    addNewerLanguageTranspilationCheck('es7', function() {
      return evalCheck('2 ** 2 == 4');
    });
    // async functions are the only new features in 'es8'
    addNewerLanguageTranspilationCheck('es8', function() {
      return evalCheck('async () => 1, true');
    });
    addNewerLanguageTranspilationCheck('es9', function() {
      return evalCheck('({...rest} = {}), true');
    });
    addNewerLanguageTranspilationCheck('es_next', function() {
      return false;  // assume it always need to transpile
    });
    return {target: transpilationTarget, map: requiresTranspilation};
  };


  /**
   * Determines whether the given language needs to be transpiled.
   * @param {string} lang
   * @param {string|undefined} module
   * @return {boolean}
   */
  goog.Transpiler.prototype.needsTranspile = function(lang, module) {
    if (goog.TRANSPILE == 'always') {
      return true;
    } else if (goog.TRANSPILE == 'never') {
      return false;
    } else if (!this.requiresTranspilation_) {
      var obj = this.createRequiresTranspilation_();
      this.requiresTranspilation_ = obj.map;
      this.transpilationTarget_ = this.transpilationTarget_ || obj.target;
    }
    if (lang in this.requiresTranspilation_) {
      if (this.requiresTranspilation_[lang]) {
        return true;
      } else if (
          goog.inHtmlDocument_() && module == 'es6' &&
          !('noModule' in goog.global.document.createElement('script'))) {
        return true;
      } else {
        return false;
      }
    } else {
      throw new Error('Unknown language mode: ' + lang);
    }
  };


  /**
   * Lazily retrieves the transpiler and applies it to the source.
   * @param {string} code JS code.
   * @param {string} path Path to the code.
   * @return {string} The transpiled code.
   */
  goog.Transpiler.prototype.transpile = function(code, path) {
    // TODO(johnplaisted): We should delete goog.transpile_ and just have this
    // function. But there's some compile error atm where goog.global is being
    // stripped incorrectly without this.
    return goog.transpile_(code, path, this.transpilationTarget_);
  };


  /** @private @final {!goog.Transpiler} */
  goog.transpiler_ = new goog.Transpiler();

  /**
   * Rewrites closing script tags in input to avoid ending an enclosing script
   * tag.
   *
   * @param {string} str
   * @return {string}
   * @private
   */
  goog.protectScriptTag_ = function(str) {
    return str.replace(/<\/(SCRIPT)/ig, '\\x3c/$1');
  };


  /**
   * A debug loader is responsible for downloading and executing javascript
   * files in an unbundled, uncompiled environment.
   *
   * This can be custimized via the setDependencyFactory method, or by
   * CLOSURE_IMPORT_SCRIPT/CLOSURE_LOAD_FILE_SYNC.
   *
   * @struct @constructor @final @private
   */
  goog.DebugLoader_ = function() {
    /** @private @const {!Object<string, !goog.Dependency>} */
    this.dependencies_ = {};
    /** @private @const {!Object<string, string>} */
    this.idToPath_ = {};
    /** @private @const {!Object<string, boolean>} */
    this.written_ = {};
    /** @private @const {!Array<!goog.Dependency>} */
    this.loadingDeps_ = [];
    /** @private {!Array<!goog.Dependency>} */
    this.depsToLoad_ = [];
    /** @private {boolean} */
    this.paused_ = false;
    /** @private {!goog.DependencyFactory} */
    this.factory_ = new goog.DependencyFactory(goog.transpiler_);
    /** @private @const {!Object<string, !Function>} */
    this.deferredCallbacks_ = {};
    /** @private @const {!Array<string>} */
    this.deferredQueue_ = [];
  };

  /**
   * @param {!Array<string>} namespaces
   * @param {function(): undefined} callback Function to call once all the
   *     namespaces have loaded.
   */
  goog.DebugLoader_.prototype.bootstrap = function(namespaces, callback) {
    var cb = callback;
    function resolve() {
      if (cb) {
        goog.global.setTimeout(cb, 0);
        cb = null;
      }
    }

    if (!namespaces.length) {
      resolve();
      return;
    }

    var deps = [];
    for (var i = 0; i < namespaces.length; i++) {
      var path = this.getPathFromDeps_(namespaces[i]);
      if (!path) {
        throw new Error('Unregonized namespace: ' + namespaces[i]);
      }
      deps.push(this.dependencies_[path]);
    }

    var require = goog.require;
    var loaded = 0;
    for (var i = 0; i < namespaces.length; i++) {
      require(namespaces[i]);
      deps[i].onLoad(function() {
        if (++loaded == namespaces.length) {
          resolve();
        }
      });
    }
  };


  /**
   * Loads the Closure Dependency file.
   *
   * Exposed a public function so CLOSURE_NO_DEPS can be set to false, base
   * loaded, setDependencyFactory called, and then this called. i.e. allows
   * custom loading of the deps file.
   */
  goog.DebugLoader_.prototype.loadClosureDeps = function() {
    // Circumvent addDependency, which would try to transpile deps.js if
    // transpile is set to always.
    var relPath = 'deps.js';
    this.depsToLoad_.push(this.factory_.createDependency(
        goog.normalizePath_(goog.basePath + relPath), relPath, [], [], {},
        false));
    this.loadDeps_();
  };


  /**
   * Notifies the debug loader when a dependency has been requested.
   *
   * @param {string} absPathOrId Path of the dependency or goog id.
   * @param {boolean=} opt_force
   */
  goog.DebugLoader_.prototype.requested = function(absPathOrId, opt_force) {
    var path = this.getPathFromDeps_(absPathOrId);
    if (path &&
        (opt_force || this.areDepsLoaded_(this.dependencies_[path].requires))) {
      var callback = this.deferredCallbacks_[path];
      if (callback) {
        delete this.deferredCallbacks_[path];
        callback();
      }
    }
  };


  /**
   * Sets the dependency factory, which can be used to create custom
   * goog.Dependency implementations to control how dependencies are loaded.
   *
   * @param {!goog.DependencyFactory} factory
   */
  goog.DebugLoader_.prototype.setDependencyFactory = function(factory) {
    this.factory_ = factory;
  };


  /**
   * Travserses the dependency graph and queues the given dependency, and all of
   * its transitive dependencies, for loading and then starts loading if not
   * paused.
   *
   * @param {string} namespace
   * @private
   */
  goog.DebugLoader_.prototype.load_ = function(namespace) {
    if (!this.getPathFromDeps_(namespace)) {
      var errorMessage = 'goog.require could not find: ' + namespace;

      goog.logToConsole_(errorMessage);
      throw Error(errorMessage);
    } else {
      var loader = this;

      var deps = [];

      /** @param {string} namespace */
      var visit = function(namespace) {
        var path = loader.getPathFromDeps_(namespace);

        if (!path) {
          throw new Error('Bad dependency path or symbol: ' + namespace);
        }

        if (loader.written_[path]) {
          return;
        }

        loader.written_[path] = true;

        var dep = loader.dependencies_[path];
        for (var i = 0; i < dep.requires.length; i++) {
          if (!goog.isProvided_(dep.requires[i])) {
            visit(dep.requires[i]);
          }
        }

        deps.push(dep);
      };

      visit(namespace);

      var wasLoading = !!this.depsToLoad_.length;
      this.depsToLoad_ = this.depsToLoad_.concat(deps);

      if (!this.paused_ && !wasLoading) {
        this.loadDeps_();
      }
    }
  };


  /**
   * Loads any queued dependencies until they are all loaded or paused.
   *
   * @private
   */
  goog.DebugLoader_.prototype.loadDeps_ = function() {
    var loader = this;
    var paused = this.paused_;

    while (this.depsToLoad_.length && !paused) {
      (function() {
        var loadCallDone = false;
        var dep = loader.depsToLoad_.shift();

        var loaded = false;
        loader.loading_(dep);

        var controller = {
          pause: function() {
            if (loadCallDone) {
              throw new Error('Cannot call pause after the call to load.');
            } else {
              paused = true;
            }
          },
          resume: function() {
            if (loadCallDone) {
              loader.resume_();
            } else {
              // Some dep called pause and then resume in the same load call.
              // Just keep running this same loop.
              paused = false;
            }
          },
          loaded: function() {
            if (loaded) {
              throw new Error('Double call to loaded.');
            }

            loaded = true;
            loader.loaded_(dep);
          },
          pending: function() {
            // Defensive copy.
            var pending = [];
            for (var i = 0; i < loader.loadingDeps_.length; i++) {
              pending.push(loader.loadingDeps_[i]);
            }
            return pending;
          },
          /**
           * @param {goog.ModuleType} type
           */
          setModuleState: function(type) {
            goog.moduleLoaderState_ = {
              type: type,
              moduleName: '',
              declareLegacyNamespace: false
            };
          },
          /** @type {function(string, string, string=)} */
          registerEs6ModuleExports: function(
              path, exports, opt_closureNamespace) {
            if (opt_closureNamespace) {
              goog.loadedModules_[opt_closureNamespace] = {
                exports: exports,
                type: goog.ModuleType.ES6,
                moduleId: opt_closureNamespace || ''
              };
            }
          },
          /** @type {function(string, ?)} */
          registerGoogModuleExports: function(moduleId, exports) {
            goog.loadedModules_[moduleId] = {
              exports: exports,
              type: goog.ModuleType.GOOG,
              moduleId: moduleId
            };
          },
          clearModuleState: function() {
            goog.moduleLoaderState_ = null;
          },
          defer: function(callback) {
            if (loadCallDone) {
              throw new Error(
                  'Cannot register with defer after the call to load.');
            }
            loader.defer_(dep, callback);
          },
          areDepsLoaded: function() {
            return loader.areDepsLoaded_(dep.requires);
          }
        };

        try {
          dep.load(controller);
        } finally {
          loadCallDone = true;
        }
      })();
    }

    if (paused) {
      this.pause_();
    }
  };


  /** @private */
  goog.DebugLoader_.prototype.pause_ = function() {
    this.paused_ = true;
  };


  /** @private */
  goog.DebugLoader_.prototype.resume_ = function() {
    if (this.paused_) {
      this.paused_ = false;
      this.loadDeps_();
    }
  };


  /**
   * Marks the given dependency as loading (load has been called but it has not
   * yet marked itself as finished). Useful for dependencies that want to know
   * what else is loading. Example: goog.modules cannot eval if there are
   * loading dependencies.
   *
   * @param {!goog.Dependency} dep
   * @private
   */
  goog.DebugLoader_.prototype.loading_ = function(dep) {
    this.loadingDeps_.push(dep);
  };


  /**
   * Marks the given dependency as having finished loading and being available
   * for require.
   *
   * @param {!goog.Dependency} dep
   * @private
   */
  goog.DebugLoader_.prototype.loaded_ = function(dep) {
    for (var i = 0; i < this.loadingDeps_.length; i++) {
      if (this.loadingDeps_[i] == dep) {
        this.loadingDeps_.splice(i, 1);
        break;
      }
    }

    for (var i = 0; i < this.deferredQueue_.length; i++) {
      if (this.deferredQueue_[i] == dep.path) {
        this.deferredQueue_.splice(i, 1);
        break;
      }
    }

    if (this.loadingDeps_.length == this.deferredQueue_.length &&
        !this.depsToLoad_.length) {
      // Something has asked to load these, but they may not be directly
      // required again later, so load them now that we know we're done loading
      // everything else. e.g. a goog module entry point.
      while (this.deferredQueue_.length) {
        this.requested(this.deferredQueue_.shift(), true);
      }
    }

    dep.loaded();
  };


  /**
   * @param {!Array<string>} pathsOrIds
   * @return {boolean}
   * @private
   */
  goog.DebugLoader_.prototype.areDepsLoaded_ = function(pathsOrIds) {
    for (var i = 0; i < pathsOrIds.length; i++) {
      var path = this.getPathFromDeps_(pathsOrIds[i]);
      if (!path ||
          (!(path in this.deferredCallbacks_) &&
           !goog.isProvided_(pathsOrIds[i]))) {
        return false;
      }
    }

    return true;
  };


  /**
   * @param {string} absPathOrId
   * @return {?string}
   * @private
   */
  goog.DebugLoader_.prototype.getPathFromDeps_ = function(absPathOrId) {
    if (absPathOrId in this.idToPath_) {
      return this.idToPath_[absPathOrId];
    } else if (absPathOrId in this.dependencies_) {
      return absPathOrId;
    } else {
      return null;
    }
  };


  /**
   * @param {!goog.Dependency} dependency
   * @param {!Function} callback
   * @private
   */
  goog.DebugLoader_.prototype.defer_ = function(dependency, callback) {
    this.deferredCallbacks_[dependency.path] = callback;
    this.deferredQueue_.push(dependency.path);
  };


  /**
   * Interface for goog.Dependency implementations to have some control over
   * loading of dependencies.
   *
   * @record
   */
  goog.LoadController = function() {};


  /**
   * Tells the controller to halt loading of more dependencies.
   */
  goog.LoadController.prototype.pause = function() {};


  /**
   * Tells the controller to resume loading of more dependencies if paused.
   */
  goog.LoadController.prototype.resume = function() {};


  /**
   * Tells the controller that this dependency has finished loading.
   *
   * This causes this to be removed from pending() and any load callbacks to
   * fire.
   */
  goog.LoadController.prototype.loaded = function() {};


  /**
   * List of dependencies on which load has been called but which have not
   * called loaded on their controller. This includes the current dependency.
   *
   * @return {!Array<!goog.Dependency>}
   */
  goog.LoadController.prototype.pending = function() {};


  /**
   * Registers an object as an ES6 module's exports so that goog.modules may
   * require it by path.
   *
   * @param {string} path Full path of the module.
   * @param {?} exports
   * @param {string=} opt_closureNamespace Closure namespace to associate with
   *     this module.
   */
  goog.LoadController.prototype.registerEs6ModuleExports = function(
      path, exports, opt_closureNamespace) {};


  /**
   * Sets the current module state.
   *
   * @param {goog.ModuleType} type Type of module.
   */
  goog.LoadController.prototype.setModuleState = function(type) {};


  /**
   * Clears the current module state.
   */
  goog.LoadController.prototype.clearModuleState = function() {};


  /**
   * Registers a callback to call once the dependency is actually requested
   * via goog.require + all of the immediate dependencies have been loaded or
   * all other files have been loaded. Allows for lazy loading until
   * require'd without pausing dependency loading, which is needed on old IE.
   *
   * @param {!Function} callback
   */
  goog.LoadController.prototype.defer = function(callback) {};


  /**
   * @return {boolean}
   */
  goog.LoadController.prototype.areDepsLoaded = function() {};


  /**
   * Basic super class for all dependencies Closure Library can load.
   *
   * This default implementation is designed to load untranspiled, non-module
   * scripts in a web broswer.
   *
   * For transpiled non-goog.module files {@see goog.TranspiledDependency}.
   * For goog.modules see {@see goog.GoogModuleDependency}.
   * For untranspiled ES6 modules {@see goog.Es6ModuleDependency}.
   *
   * @param {string} path Absolute path of this script.
   * @param {string} relativePath Path of this script relative to goog.basePath.
   * @param {!Array<string>} provides goog.provided or goog.module symbols
   *     in this file.
   * @param {!Array<string>} requires goog symbols or relative paths to Closure
   *     this depends on.
   * @param {!Object<string, string>} loadFlags
   * @struct @constructor
   */
  goog.Dependency = function(
      path, relativePath, provides, requires, loadFlags) {
    /** @const */
    this.path = path;
    /** @const */
    this.relativePath = relativePath;
    /** @const */
    this.provides = provides;
    /** @const */
    this.requires = requires;
    /** @const */
    this.loadFlags = loadFlags;
    /** @private {boolean} */
    this.loaded_ = false;
    /** @private {!Array<function()>} */
    this.loadCallbacks_ = [];
  };


  /**
   * @return {string} The pathname part of this dependency's path if it is a
   *     URI.
   */
  goog.Dependency.prototype.getPathName = function() {
    var pathName = this.path;
    var protocolIndex = pathName.indexOf('://');
    if (protocolIndex >= 0) {
      pathName = pathName.substring(protocolIndex + 3);
      var slashIndex = pathName.indexOf('/');
      if (slashIndex >= 0) {
        pathName = pathName.substring(slashIndex + 1);
      }
    }
    return pathName;
  };


  /**
   * @param {function()} callback Callback to fire as soon as this has loaded.
   * @final
   */
  goog.Dependency.prototype.onLoad = function(callback) {
    if (this.loaded_) {
      callback();
    } else {
      this.loadCallbacks_.push(callback);
    }
  };


  /**
   * Marks this dependency as loaded and fires any callbacks registered with
   * onLoad.
   * @final
   */
  goog.Dependency.prototype.loaded = function() {
    this.loaded_ = true;
    var callbacks = this.loadCallbacks_;
    this.loadCallbacks_ = [];
    for (var i = 0; i < callbacks.length; i++) {
      callbacks[i]();
    }
  };


  /**
   * Whether or not document.written / appended script tags should be deferred.
   *
   * @private {boolean}
   */
  goog.Dependency.defer_ = false;


  /**
   * Map of script ready / state change callbacks. Old IE cannot handle putting
   * these properties on goog.global.
   *
   * @private @const {!Object<string, function(?):undefined>}
   */
  goog.Dependency.callbackMap_ = {};


  /**
   * @param {function(...?):?} callback
   * @return {string}
   * @private
   */
  goog.Dependency.registerCallback_ = function(callback) {
    var key = Math.random().toString(32);
    goog.Dependency.callbackMap_[key] = callback;
    return key;
  };


  /**
   * @param {string} key
   * @private
   */
  goog.Dependency.unregisterCallback_ = function(key) {
    delete goog.Dependency.callbackMap_[key];
  };


  /**
   * @param {string} key
   * @param {...?} var_args
   * @private
   * @suppress {unusedPrivateMembers}
   */
  goog.Dependency.callback_ = function(key, var_args) {
    if (key in goog.Dependency.callbackMap_) {
      var callback = goog.Dependency.callbackMap_[key];
      var args = [];
      for (var i = 1; i < arguments.length; i++) {
        args.push(arguments[i]);
      }
      callback.apply(undefined, args);
    } else {
      var errorMessage = 'Callback key ' + key +
          ' does not exist (was base.js loaded more than once?).';
      throw Error(errorMessage);
    }
  };


  /**
   * Starts loading this dependency. This dependency can pause loading if it
   * needs to and resume it later via the controller interface.
   *
   * When this is loaded it should call controller.loaded(). Note that this will
   * end up calling the loaded method of this dependency; there is no need to
   * call it explicitly.
   *
   * @param {!goog.LoadController} controller
   */
  goog.Dependency.prototype.load = function(controller) {
    if (goog.global.CLOSURE_IMPORT_SCRIPT) {
      if (goog.global.CLOSURE_IMPORT_SCRIPT(this.path)) {
        controller.loaded();
      } else {
        controller.pause();
      }
      return;
    }

    if (!goog.inHtmlDocument_()) {
      goog.logToConsole_(
          'Cannot use default debug loader outside of HTML documents.');
      if (this.relativePath == 'deps.js') {
        // Some old code is relying on base.js auto loading deps.js failing with
        // no error before later setting CLOSURE_IMPORT_SCRIPT.
        // CLOSURE_IMPORT_SCRIPT should be set *before* base.js is loaded, or
        // CLOSURE_NO_DEPS set to true.
        goog.logToConsole_(
            'Consider setting CLOSURE_IMPORT_SCRIPT before loading base.js, ' +
            'or setting CLOSURE_NO_DEPS to true.');
        controller.loaded();
      } else {
        controller.pause();
      }
      return;
    }

    /** @type {!HTMLDocument} */
    var doc = goog.global.document;

    // If the user tries to require a new symbol after document load,
    // something has gone terribly wrong. Doing a document.write would
    // wipe out the page. This does not apply to the CSP-compliant method
    // of writing script tags.
    if (doc.readyState == 'complete' &&
        !goog.ENABLE_CHROME_APP_SAFE_SCRIPT_LOADING) {
      // Certain test frameworks load base.js multiple times, which tries
      // to write deps.js each time. If that happens, just fail silently.
      // These frameworks wipe the page between each load of base.js, so this
      // is OK.
      var isDeps = /\bdeps.js$/.test(this.path);
      if (isDeps) {
        controller.loaded();
        return;
      } else {
        throw Error('Cannot write "' + this.path + '" after document load');
      }
    }

    if (!goog.ENABLE_CHROME_APP_SAFE_SCRIPT_LOADING &&
        goog.isDocumentLoading_()) {
      var key = goog.Dependency.registerCallback_(function(script) {
        if (!goog.DebugLoader_.IS_OLD_IE_ || script.readyState == 'complete') {
          goog.Dependency.unregisterCallback_(key);
          controller.loaded();
        }
      });
      var nonceAttr = !goog.DebugLoader_.IS_OLD_IE_ && goog.getScriptNonce() ?
          ' nonce="' + goog.getScriptNonce() + '"' :
          '';
      var event =
          goog.DebugLoader_.IS_OLD_IE_ ? 'onreadystatechange' : 'onload';
      var defer = goog.Dependency.defer_ ? 'defer' : '';
      doc.write(
          '<script src="' + this.path + '" ' + event +
          '="goog.Dependency.callback_(\'' + key +
          '\', this)" type="text/javascript" ' + defer + nonceAttr + '><' +
          '/script>');
    } else {
      var scriptEl =
          /** @type {!HTMLScriptElement} */ (doc.createElement('script'));
      scriptEl.defer = goog.Dependency.defer_;
      scriptEl.async = false;
      scriptEl.type = 'text/javascript';

      // If CSP nonces are used, propagate them to dynamically created scripts.
      // This is necessary to allow nonce-based CSPs without 'strict-dynamic'.
      var nonce = goog.getScriptNonce();
      if (nonce) {
        scriptEl.setAttribute('nonce', nonce);
      }

      if (goog.DebugLoader_.IS_OLD_IE_) {
        // Execution order is not guaranteed on old IE, halt loading and write
        // these scripts one at a time, after each loads.
        controller.pause();
        scriptEl.onreadystatechange = function() {
          if (scriptEl.readyState == 'loaded' ||
              scriptEl.readyState == 'complete') {
            controller.loaded();
            controller.resume();
          }
        };
      } else {
        scriptEl.onload = function() {
          scriptEl.onload = null;
          controller.loaded();
        };
      }

      scriptEl.src = this.path;
      doc.head.appendChild(scriptEl);
    }
  };


  /**
   * @param {string} path Absolute path of this script.
   * @param {string} relativePath Path of this script relative to goog.basePath.
   * @param {!Array<string>} provides Should be an empty array.
   *     TODO(johnplaisted) add support for adding closure namespaces to ES6
   *     modules for interop purposes.
   * @param {!Array<string>} requires goog symbols or relative paths to Closure
   *     this depends on.
   * @param {!Object<string, string>} loadFlags
   * @struct @constructor
   * @extends {goog.Dependency}
   */
  goog.Es6ModuleDependency = function(
      path, relativePath, provides, requires, loadFlags) {
    goog.Es6ModuleDependency.base(
        this, 'constructor', path, relativePath, provides, requires, loadFlags);
  };
  goog.inherits(goog.Es6ModuleDependency, goog.Dependency);


  /** @override */
  goog.Es6ModuleDependency.prototype.load = function(controller) {
    if (goog.global.CLOSURE_IMPORT_SCRIPT) {
      if (goog.global.CLOSURE_IMPORT_SCRIPT(this.path)) {
        controller.loaded();
      } else {
        controller.pause();
      }
      return;
    }

    if (!goog.inHtmlDocument_()) {
      goog.logToConsole_(
          'Cannot use default debug loader outside of HTML documents.');
      controller.pause();
      return;
    }

    /** @type {!HTMLDocument} */
    var doc = goog.global.document;

    var dep = this;

    // TODO(johnplaisted): Does document.writing really speed up anything? Any
    // difference between this and just waiting for interactive mode and then
    // appending?
    function write(src, contents) {
      if (contents) {
        doc.write(
            '<script type="module" crossorigin>' + contents + '</' +
            'script>');
      } else {
        doc.write(
            '<script type="module" crossorigin src="' + src + '"></' +
            'script>');
      }
    }

    function append(src, contents) {
      var scriptEl =
          /** @type {!HTMLScriptElement} */ (doc.createElement('script'));
      scriptEl.defer = true;
      scriptEl.async = false;
      scriptEl.type = 'module';
      scriptEl.setAttribute('crossorigin', true);

      // If CSP nonces are used, propagate them to dynamically created scripts.
      // This is necessary to allow nonce-based CSPs without 'strict-dynamic'.
      var nonce = goog.getScriptNonce();
      if (nonce) {
        scriptEl.setAttribute('nonce', nonce);
      }

      if (contents) {
        scriptEl.textContent = contents;
      } else {
        scriptEl.src = src;
      }

      doc.head.appendChild(scriptEl);
    }

    var create;

    if (goog.isDocumentLoading_()) {
      create = write;
      // We can ONLY call document.write if we are guaranteed that any
      // non-module script tags document.written after this are deferred.
      // Small optimization, in theory document.writing is faster.
      goog.Dependency.defer_ = true;
    } else {
      create = append;
    }

    // Write 4 separate tags here:
    // 1) Sets the module state at the correct time (just before execution).
    // 2) A src node for this, which just hopefully lets the browser load it a
    //    little early (no need to parse #3).
    // 3) Import the module and register it.
    // 4) Clear the module state at the correct time. Guarnteed to run even
    //    if there is an error in the module (#3 will not run if there is an
    //    error in the module).
    var beforeKey = goog.Dependency.registerCallback_(function() {
      goog.Dependency.unregisterCallback_(beforeKey);
      controller.setModuleState(goog.ModuleType.ES6);
    });
    create(undefined, 'goog.Dependency.callback_("' + beforeKey + '")');

    // TODO(johnplaisted): Does this really speed up anything?
    create(this.path, undefined);

    var registerKey = goog.Dependency.registerCallback_(function(exports) {
      goog.Dependency.unregisterCallback_(registerKey);
      controller.registerEs6ModuleExports(
          dep.path, exports, goog.moduleLoaderState_.moduleName);
    });
    create(
        undefined,
        'import * as m from "' + this.path + '"; goog.Dependency.callback_("' +
            registerKey + '", m)');

    var afterKey = goog.Dependency.registerCallback_(function() {
      goog.Dependency.unregisterCallback_(afterKey);
      controller.clearModuleState();
      controller.loaded();
    });
    create(undefined, 'goog.Dependency.callback_("' + afterKey + '")');
  };


  /**
   * Superclass of any dependency that needs to be loaded into memory,
   * transformed, and then eval'd (goog.modules and transpiled files).
   *
   * @param {string} path Absolute path of this script.
   * @param {string} relativePath Path of this script relative to goog.basePath.
   * @param {!Array<string>} provides goog.provided or goog.module symbols
   *     in this file.
   * @param {!Array<string>} requires goog symbols or relative paths to Closure
   *     this depends on.
   * @param {!Object<string, string>} loadFlags
   * @struct @constructor @abstract
   * @extends {goog.Dependency}
   */
  goog.TransformedDependency = function(
      path, relativePath, provides, requires, loadFlags) {
    goog.TransformedDependency.base(
        this, 'constructor', path, relativePath, provides, requires, loadFlags);
    /** @private {?string} */
    this.contents_ = null;

    /**
     * Whether to lazily make the synchronous XHR (when goog.require'd) or make
     * the synchronous XHR when initially loading. On FireFox 61 there is a bug
     * where an ES6 module cannot make a synchronous XHR (rather, it can, but if
     * it does then no other ES6 modules will load after).
     *
     * tl;dr we lazy load due to bugs on older browsers and eager load due to
     * bugs on newer ones.
     *
     * https://bugzilla.mozilla.org/show_bug.cgi?id=1477090
     *
     * @private @const {boolean}
     */
    this.lazyFetch_ = !goog.inHtmlDocument_() ||
        !('noModule' in goog.global.document.createElement('script'));
  };
  goog.inherits(goog.TransformedDependency, goog.Dependency);


  /** @override */
  goog.TransformedDependency.prototype.load = function(controller) {
    var dep = this;

    function fetch() {
      dep.contents_ = goog.loadFileSync_(dep.path);

      if (dep.contents_) {
        dep.contents_ = dep.transform(dep.contents_);
        if (dep.contents_) {
          dep.contents_ += '\n//# sourceURL=' + dep.path;
        }
      }
    }

    if (goog.global.CLOSURE_IMPORT_SCRIPT) {
      fetch();
      if (this.contents_ &&
          goog.global.CLOSURE_IMPORT_SCRIPT('', this.contents_)) {
        this.contents_ = null;
        controller.loaded();
      } else {
        controller.pause();
      }
      return;
    }


    var isEs6 = this.loadFlags['module'] == goog.ModuleType.ES6;

    if (!this.lazyFetch_) {
      fetch();
    }

    function load() {
      if (dep.lazyFetch_) {
        fetch();
      }

      if (!dep.contents_) {
        // loadFileSync_ or transform are responsible. Assume they logged an
        // error.
        return;
      }

      if (isEs6) {
        controller.setModuleState(goog.ModuleType.ES6);
      }

      var namespace;

      try {
        var contents = dep.contents_;
        dep.contents_ = null;
        goog.globalEval(contents);
        if (isEs6) {
          namespace = goog.moduleLoaderState_.moduleName;
        }
      } finally {
        if (isEs6) {
          controller.clearModuleState();
        }
      }

      if (isEs6) {
        // Due to circular dependencies this may not be available for require
        // right now.
        goog.global['$jscomp']['require']['ensure'](
            [dep.getPathName()], function() {
              controller.registerEs6ModuleExports(
                  dep.path,
                  goog.global['$jscomp']['require'](dep.getPathName()),
                  namespace);
            });
      }

      controller.loaded();
    }

    // Do not fetch now; in FireFox 47 the synchronous XHR doesn't block all
    // events. If we fetched now and then document.write'd the contents the
    // document.write would be an eval and would execute too soon! Instead write
    // a script tag to fetch and eval synchronously at the correct time.
    function fetchInOwnScriptThenLoad() {
      /** @type {!HTMLDocument} */
      var doc = goog.global.document;

      var key = goog.Dependency.registerCallback_(function() {
        goog.Dependency.unregisterCallback_(key);
        load();
      });

      doc.write(
          '<script type="text/javascript">' +
          goog.protectScriptTag_('goog.Dependency.callback_("' + key + '");') +
          '</' +
          'script>');
    }

    // If one thing is pending it is this.
    var anythingElsePending = controller.pending().length > 1;

    // If anything else is loading we need to lazy load due to bugs in old IE.
    // Specifically script tags with src and script tags with contents could
    // execute out of order if document.write is used, so we cannot use
    // document.write. Do not pause here; it breaks old IE as well.
    var useOldIeWorkAround =
        anythingElsePending && goog.DebugLoader_.IS_OLD_IE_;

    // Additionally if we are meant to defer scripts but the page is still
    // loading (e.g. an ES6 module is loading) then also defer. Or if we are
    // meant to defer and anything else is pending then defer (those may be
    // scripts that did not need transformation and are just script tags with
    // defer set to true, and we need to evaluate after that deferred script).
    var needsAsyncLoading = goog.Dependency.defer_ &&
        (anythingElsePending || goog.isDocumentLoading_());

    if (useOldIeWorkAround || needsAsyncLoading) {
      // Note that we only defer when we have to rather than 100% of the time.
      // Always defering would work, but then in theory the order of
      // goog.require calls would then matter. We want to enforce that most of
      // the time the order of the require calls does not matter.
      controller.defer(function() {
        load();
      });
      return;
    }
    // TODO(johnplaisted): Externs are missing onreadystatechange for
    // HTMLDocument.
    /** @type {?} */
    var doc = goog.global.document;

    var isInternetExplorer =
        goog.inHtmlDocument_() && 'ActiveXObject' in goog.global;

    // Don't delay in any version of IE. There's bug around this that will
    // cause out of order script execution. This means that on older IE ES6
    // modules will load too early (while the document is still loading + the
    // dom is not available). The other option is to load too late (when the
    // document is complete and the onload even will never fire). This seems
    // to be the lesser of two evils as scripts already act like the former.
    if (isEs6 && goog.inHtmlDocument_() && goog.isDocumentLoading_() &&
        !isInternetExplorer) {
      goog.Dependency.defer_ = true;
      // Transpiled ES6 modules still need to load like regular ES6 modules,
      // aka only after the document is interactive.
      controller.pause();
      var oldCallback = doc.onreadystatechange;
      doc.onreadystatechange = function() {
        if (doc.readyState == 'interactive') {
          doc.onreadystatechange = oldCallback;
          load();
          controller.resume();
        }
        if (goog.isFunction(oldCallback)) {
          oldCallback.apply(undefined, arguments);
        }
      };
    } else {
      // Always eval on old IE.
      if (goog.DebugLoader_.IS_OLD_IE_ || !goog.inHtmlDocument_() ||
          !goog.isDocumentLoading_()) {
        load();
      } else {
        fetchInOwnScriptThenLoad();
      }
    }
  };


  /**
   * @param {string} contents
   * @return {string}
   * @abstract
   */
  goog.TransformedDependency.prototype.transform = function(contents) {};


  /**
   * Any non-goog.module dependency which needs to be transpiled before eval.
   *
   * @param {string} path Absolute path of this script.
   * @param {string} relativePath Path of this script relative to goog.basePath.
   * @param {!Array<string>} provides goog.provided or goog.module symbols
   *     in this file.
   * @param {!Array<string>} requires goog symbols or relative paths to Closure
   *     this depends on.
   * @param {!Object<string, string>} loadFlags
   * @param {!goog.Transpiler} transpiler
   * @struct @constructor
   * @extends {goog.TransformedDependency}
   */
  goog.TranspiledDependency = function(
      path, relativePath, provides, requires, loadFlags, transpiler) {
    goog.TranspiledDependency.base(
        this, 'constructor', path, relativePath, provides, requires, loadFlags);
    /** @protected @const*/
    this.transpiler = transpiler;
  };
  goog.inherits(goog.TranspiledDependency, goog.TransformedDependency);


  /** @override */
  goog.TranspiledDependency.prototype.transform = function(contents) {
    // Transpile with the pathname so that ES6 modules are domain agnostic.
    return this.transpiler.transpile(contents, this.getPathName());
  };


  /**
   * A goog.module, transpiled or not. Will always perform some minimal
   * transformation even when not transpiled to wrap in a goog.loadModule
   * statement.
   *
   * @param {string} path Absolute path of this script.
   * @param {string} relativePath Path of this script relative to goog.basePath.
   * @param {!Array<string>} provides goog.provided or goog.module symbols
   *     in this file.
   * @param {!Array<string>} requires goog symbols or relative paths to Closure
   *     this depends on.
   * @param {!Object<string, string>} loadFlags
   * @param {boolean} needsTranspile
   * @param {!goog.Transpiler} transpiler
   * @struct @constructor
   * @extends {goog.TransformedDependency}
   */
  goog.GoogModuleDependency = function(
      path, relativePath, provides, requires, loadFlags, needsTranspile,
      transpiler) {
    goog.GoogModuleDependency.base(
        this, 'constructor', path, relativePath, provides, requires, loadFlags);
    /** @private @const */
    this.needsTranspile_ = needsTranspile;
    /** @private @const */
    this.transpiler_ = transpiler;
  };
  goog.inherits(goog.GoogModuleDependency, goog.TransformedDependency);


  /** @override */
  goog.GoogModuleDependency.prototype.transform = function(contents) {
    if (this.needsTranspile_) {
      contents = this.transpiler_.transpile(contents, this.getPathName());
    }

    if (!goog.LOAD_MODULE_USING_EVAL || !goog.isDef(goog.global.JSON)) {
      return '' +
          'goog.loadModule(function(exports) {' +
          '"use strict";' + contents +
          '\n' +  // terminate any trailing single line comment.
          ';return exports' +
          '});' +
          '\n//# sourceURL=' + this.path + '\n';
    } else {
      return '' +
          'goog.loadModule(' +
          goog.global.JSON.stringify(
              contents + '\n//# sourceURL=' + this.path + '\n') +
          ');';
    }
  };


  /**
   * Whether the browser is IE9 or earlier, which needs special handling
   * for deferred modules.
   * @const @private {boolean}
   */
  goog.DebugLoader_.IS_OLD_IE_ = !!(
      !goog.global.atob && goog.global.document && goog.global.document['all']);


  /**
   * @param {string} relPath
   * @param {!Array<string>|undefined} provides
   * @param {!Array<string>} requires
   * @param {boolean|!Object<string>=} opt_loadFlags
   * @see goog.addDependency
   */
  goog.DebugLoader_.prototype.addDependency = function(
      relPath, provides, requires, opt_loadFlags) {
    provides = provides || [];
    relPath = relPath.replace(/\\/g, '/');
    var path = goog.normalizePath_(goog.basePath + relPath);
    if (!opt_loadFlags || typeof opt_loadFlags === 'boolean') {
      opt_loadFlags = opt_loadFlags ? {'module': goog.ModuleType.GOOG} : {};
    }
    var dep = this.factory_.createDependency(
        path, relPath, provides, requires, opt_loadFlags,
        goog.transpiler_.needsTranspile(
            opt_loadFlags['lang'] || 'es3', opt_loadFlags['module']));
    this.dependencies_[path] = dep;
    for (var i = 0; i < provides.length; i++) {
      this.idToPath_[provides[i]] = path;
    }
    this.idToPath_[relPath] = path;
  };


  /**
   * Creates goog.Dependency instances for the debug loader to load.
   *
   * Should be overridden to have the debug loader use custom subclasses of
   * goog.Dependency.
   *
   * @param {!goog.Transpiler} transpiler
   * @struct @constructor
   */
  goog.DependencyFactory = function(transpiler) {
    /** @protected @const */
    this.transpiler = transpiler;
  };


  /**
   * @param {string} path Absolute path of the file.
   * @param {string} relativePath Path relative to closure’s base.js.
   * @param {!Array<string>} provides Array of provided goog.provide/module ids.
   * @param {!Array<string>} requires Array of required goog.provide/module /
   *     relative ES6 module paths.
   * @param {!Object<string, string>} loadFlags
   * @param {boolean} needsTranspile True if the file needs to be transpiled
   *     per the goog.Transpiler.
   * @return {!goog.Dependency}
   */
  goog.DependencyFactory.prototype.createDependency = function(
      path, relativePath, provides, requires, loadFlags, needsTranspile) {

    if (loadFlags['module'] == goog.ModuleType.GOOG) {
      return new goog.GoogModuleDependency(
          path, relativePath, provides, requires, loadFlags, needsTranspile,
          this.transpiler);
    } else if (needsTranspile) {
      return new goog.TranspiledDependency(
          path, relativePath, provides, requires, loadFlags, this.transpiler);
    } else {
      if (loadFlags['module'] == goog.ModuleType.ES6) {
        return new goog.Es6ModuleDependency(
            path, relativePath, provides, requires, loadFlags);
      } else {
        return new goog.Dependency(
            path, relativePath, provides, requires, loadFlags);
      }
    }
  };


  /** @private @const */
  goog.debugLoader_ = new goog.DebugLoader_();


  /**
   * Loads the Closure Dependency file.
   *
   * Exposed a public function so CLOSURE_NO_DEPS can be set to false, base
   * loaded, setDependencyFactory called, and then this called. i.e. allows
   * custom loading of the deps file.
   */
  goog.loadClosureDeps = function() {
    goog.debugLoader_.loadClosureDeps();
  };


  /**
   * Sets the dependency factory, which can be used to create custom
   * goog.Dependency implementations to control how dependencies are loaded.
   *
   * Note: if you wish to call this function and provide your own implemnetation
   * it is a wise idea to set CLOSURE_NO_DEPS to true, otherwise the dependency
   * file and all of its goog.addDependency calls will use the default factory.
   * You can call goog.loadClosureDeps to load the Closure dependency file
   * later, after your factory is injected.
   *
   * @param {!goog.DependencyFactory} factory
   */
  goog.setDependencyFactory = function(factory) {
    goog.debugLoader_.setDependencyFactory(factory);
  };


  if (!goog.global.CLOSURE_NO_DEPS) {
    goog.debugLoader_.loadClosureDeps();
  }


  /**
   * Bootstraps the given namespaces and calls the callback once they are
   * available either via goog.require. This is a replacement for using
   * `goog.require` to bootstrap Closure JavaScript. Previously a `goog.require`
   * in an HTML file would guarantee that the require'd namespace was available
   * in the next immediate script tag. With ES6 modules this no longer a
   * guarantee.
   *
   * @param {!Array<string>} namespaces
   * @param {function(): ?} callback Function to call once all the namespaces
   *     have loaded. Always called asynchronously.
   */
  goog.bootstrap = function(namespaces, callback) {
    goog.debugLoader_.bootstrap(namespaces, callback);
  };
}