CLI support for enableConditionalDirectives.

BUG=
R=brianwilkerson@google.com

Review URL: https://codereview.chromium.org/1778683004 .

pkg/analyzer_cli/lib/src/driver.dart

@@ -271,6 +271,10 @@ class Driver implements CommandLineStarter {
     if (options.enableSuperMixins != _previousOptions.enableSuperMixins) {
       return false;
     }
+    if (options.enableConditionalDirectives !=
+        _previousOptions.enableConditionalDirectives) {
+      return false;
+    }
     return true;
   }
 
@@ -579,6 +583,8 @@ class Driver implements CommandLineStarter {
     contextOptions.hint = !options.disableHints;
     contextOptions.enableStrictCallChecks = options.enableStrictCallChecks;
     contextOptions.enableSuperMixins = options.enableSuperMixins;
+    contextOptions.enableConditionalDirectives =
+        options.enableConditionalDirectives;
     contextOptions.generateImplicitErrors = options.showPackageWarnings;
     contextOptions.generateSdkErrors = options.showSdkWarnings;
     contextOptions.lint = options.lints;

pkg/analyzer_cli/lib/src/options.dart

@@ -45,6 +45,9 @@ class CommandLineOptions {
   /// Whether to display version information
   final bool displayVersion;
 
+  /// Whether to enable conditional directives (DEP 40).
+  final bool enableConditionalDirectives;
+
   /// Whether to enable null-aware operators (DEP 9).
   final bool enableNullAwareOperators;
 
@@ -128,6 +131,7 @@ class CommandLineOptions {
         analysisOptionsFile = args['options'],
         disableHints = args['no-hints'],
         displayVersion = args['version'],
+        enableConditionalDirectives = args['enable-conditional-directives'],
         enableNullAwareOperators = args['enable-null-aware-operators'],
         enableStrictCallChecks = args['enable-strict-call-checks'],
         enableSuperMixins = args['supermixin'],
@@ -335,6 +339,11 @@ class CommandLineOptions {
           defaultsTo: false,
           negatable: false,
           hide: true)
+      ..addFlag('enable-conditional-directives',
+          help: 'Enable support for conditional directives (DEP 40).',
+          defaultsTo: false,
+          negatable: false,
+          hide: true)
       ..addFlag('enable-null-aware-operators',
           help: 'Enable support for null-aware operators (DEP 9).',
           defaultsTo: false,

pkg/analyzer_cli/test/options_test.dart

@@ -25,6 +25,7 @@ main() {
         expect(options.displayVersion, isFalse);
         expect(options.enableStrictCallChecks, isFalse);
         expect(options.enableSuperMixins, isFalse);
+        expect(options.enableConditionalDirectives, isFalse);
         expect(options.enableTypeChecks, isFalse);
         expect(options.hintsAreFatal, isFalse);
         expect(options.ignoreUnrecognizedFlags, isFalse);