Adding supported checks and flags to window.performance.

sdk/lib/html/dartium/html_dartium.dart

Index: sdk/lib/html/dartium/html_dartium.dart
diff --git a/sdk/lib/html/dartium/html_dartium.dart b/sdk/lib/html/dartium/html_dartium.dart
index 1951b7c419a3d30da65aacfd46adb5faa25c6b25..9907de65655feb669728c8903c5b42c11e9e2c81 100644
--- a/sdk/lib/html/dartium/html_dartium.dart
+++ b/sdk/lib/html/dartium/html_dartium.dart
@@ -18366,9 +18366,17 @@ class ParamElement extends _Element_Merged {
 
 
 /// @domName Performance
+@SupportedBrowser(SupportedBrowser.CHROME)
+@SupportedBrowser(SupportedBrowser.FIREFOX)
+@SupportedBrowser(SupportedBrowser.IE)
 class Performance extends EventTarget {
   Performance.internal() : super.internal();
 
+  /**
+   * Checks if this type is supported on the current platform
+   */
+  static bool get supported => true;
+
 
   /** @domName Performance.memory */
   MemoryInfo get memory native "Performance_memory_Getter";
@@ -25793,6 +25801,9 @@ class Window extends EventTarget implements WindowBase {
 
 
   /** @domName DOMWindow.performance */
+  @SupportedBrowser(SupportedBrowser.CHROME)
+  @SupportedBrowser(SupportedBrowser.FIREFOX)
+  @SupportedBrowser(SupportedBrowser.IE)
   Performance get performance native "DOMWindow_performance_Getter";