Adding supported checks and flags to window.performance.

sdk/lib/html/dart2js/html_dart2js.dart

 library html;
 
 import 'dart:async';
 import 'dart:collection';
 import 'dart:html_common';
 import 'dart:indexed_db';
 import 'dart:isolate';
 import 'dart:json' as json;
 import 'dart:math';
 import 'dart:svg' as svg;
@@ skipping 15496 matching lines @@
 
   /// @domName HTMLParamElement.value; @docsEditable true
   String value;
 }
 // Copyright (c) 2012, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 
 /// @domName Performance; @docsEditable true
+@SupportedBrowser(SupportedBrowser.CHROME)
+@SupportedBrowser(SupportedBrowser.FIREFOX)
+@SupportedBrowser(SupportedBrowser.IE)
 class Performance extends EventTarget native "*Performance" {
 
+  /**
+   * Checks if this type is supported on the current platform

[Emily Fortuna, 2013/01/11 21:16:12]

nit: end in a "." and this could probably be a one line comment: /** stuff */

[blois, 2013/01/11 21:28:02]

Done.

+   */
+  static bool get supported => JS('bool', '!!(window.performance)');
+
   /// @domName Performance.memory; @docsEditable true
   final MemoryInfo memory;
 
   /// @domName Performance.navigation; @docsEditable true
   final PerformanceNavigation navigation;
 
   /// @domName Performance.timing; @docsEditable true
   final PerformanceTiming timing;
 
   /// @domName Performance.now; @docsEditable true
@@ skipping 5989 matching lines @@
   /// @domName Window.pageYOffset; @docsEditable true
   final int pageYOffset;
 
   /// @domName Window.parent; @docsEditable true
   WindowBase get parent => _convertNativeToDart_Window(this._parent);
   @JSName('parent')
   @Creates('Window|=Object') @Returns('Window|=Object')
   final dynamic _parent;
 
   /// @domName Window.performance; @docsEditable true
+  @SupportedBrowser(SupportedBrowser.CHROME) @SupportedBrowser(SupportedBrowser.FIREFOX) @SupportedBrowser(SupportedBrowser.IE)
   final Performance performance;
 
   /// @domName Window.personalbar; @docsEditable true
   final BarInfo personalbar;
 
   /// @domName Window.screen; @docsEditable true
   final Screen screen;
 
   /// @domName Window.screenLeft; @docsEditable true
   final int screenLeft;
@@ skipping 5453 matching lines @@
       _position = nextPosition;
       return true;
     }
     _current = null;
     _position = _array.length;
     return false;
   }
 
   T get current => _current;
 }