Adding supported checks and flags to window.performance.

sdk/lib/html/dart2js/html_dart2js.dart

Index: sdk/lib/html/dart2js/html_dart2js.dart
diff --git a/sdk/lib/html/dart2js/html_dart2js.dart b/sdk/lib/html/dart2js/html_dart2js.dart
index 2a525136f049e5697bf5105e4fd405cce3036139..980a73e7dcb5a3f6ed604b6d340a89a3e45a5eee 100644
--- a/sdk/lib/html/dart2js/html_dart2js.dart
+++ b/sdk/lib/html/dart2js/html_dart2js.dart
@@ -15514,8 +15514,16 @@ class ParamElement extends Element native "*HTMLParamElement" {
 
 
 /// @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;
 
@@ -21525,6 +21533,7 @@ class Window extends EventTarget implements WindowBase native "@*DOMWindow" {
   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