remove workarounds for lack of domain state tracking

lighthouse-core/gather/connections/connection.js

@@ -100,7 +100,8 @@ class Connection {
       // handleRawError returns or throws synchronously; wrap to put into promise chain.
       return callback.resolve(Promise.resolve().then(_ => {
         if (object.error) {
-          return this.handleRawError(object.error, callback.method);
+          log.formatProtocol('method <= browser ERR', {method: callback.method}, 'error');
+          throw new Error(`Protocol error (${callback.method}): ${object.error.message}`);
         }
 
         log.formatProtocol('method <= browser OK',
@@ -113,27 +114,6 @@ class Connection {
     this.emitNotification(object.method, object.params);
   }
 
-  /**
-   * Handles error responses from the protocol, absorbing errors we don't care
-   * about and throwing on the rest.
-   *
-   * Currently the only error ignored is from defensive calls of `DOM.disable`
-   * when already disabled.
-   * @param {{message: string}} error
-   * @param {string} method Protocol method that received the error response.
-   * @throws {Error}
-   * @protected
-   */
-  handleRawError(error, method) {
-    // We proactively disable the DOM domain. Ignore any errors.
-    if (error.message && error.message.includes('DOM agent hasn\'t been enabled')) {
-      return;
-    }
-
-    log.formatProtocol('method <= browser ERR', {method}, 'error');
-    throw new Error(`Protocol error (${method}): ${error.message}`);
-  }
-
   /**
    * @param {!string} method
    * @param {!Object} params

lighthouse-core/gather/driver.js

@@ -559,12 +559,19 @@ class Driver {
       options: 'sampling-frequency=10000'  // 1000 is default and too slow.
     };
 
-    // Disable any domains that could interfere or add overhead to the trace
-    return this.sendCommand('Debugger.disable')
-      .then(_ => this.sendCommand('CSS.disable'))
-      .then(_ => this.sendCommand('DOM.disable'))
-      // Enable Page domain to wait for Page.loadEventFired
-      .then(_ => this.sendCommand('Page.enable'))
+    // Check any domains that could interfere with or add overhead to the trace.
+    if (this.isDomainEnabled('Debugger')) {
+      throw new Error('Debugger domain enabled when starting trace');
+    }
+    if (this.isDomainEnabled('CSS')) {
+      throw new Error('CSS domain enabled when starting trace');
+    }
+    if (this.isDomainEnabled('DOM')) {
+      throw new Error('DOM domain enabled when starting trace');
+    }
+
+    // Enable Page domain to wait for Page.loadEventFired
+    return this.sendCommand('Page.enable')
       .then(_ => this.sendCommand('Tracing.start', tracingOpts));
   }
 
@@ -583,9 +590,6 @@ class Driver {
 
   _readTraceFromStream(streamHandle) {
     return new Promise((resolve, reject) => {
-      // COMPAT: We've found `result` not retaining its value in this scenario when it's
-      // declared with `let`. Observed in Chrome 50 and 52. While investigating the V8 bug
-      // further, we'll use a plain `var` declaration.
       let isEOF = false;
       let result = '';
 

lighthouse-core/gather/gatherers/styles.js

@@ -121,12 +121,10 @@ class Styles extends Gatherer {
       Promise.all(contentPromises).then(styleHeaders => {
         driver.off('CSS.styleSheetAdded', this._onStyleSheetAdded);
         driver.off('CSS.styleSheetRemoved', this._onStyleSheetRemoved);
-        resolve(styleHeaders);
-        // Currently both CSSUsage and Styles use these domains, so let it disable there.
-        // TODO: have a better way to specify used domains
-        // return driver.sendCommand('CSS.disable')
-        //   .then(_ => driver.sendCommand('DOM.disable'))
-        //   .then(_ => resolve(styleHeaders));
+
+        return driver.sendCommand('CSS.disable')
+          .then(_ => driver.sendCommand('DOM.disable'))
+          .then(_ => resolve(styleHeaders));
       }).catch(err => reject(err));
     });
   }