Adding support checks for WebSocket.

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 d69dd9bd9223d3863e7c9f1fd85798d54124418d..768ef7116d8682d10875f6e7ab95cbec208b86eb 100644
--- a/sdk/lib/html/dart2js/html_dart2js.dart
+++ b/sdk/lib/html/dart2js/html_dart2js.dart
@@ -21071,12 +21071,21 @@ class WebKitNamedFlow extends EventTarget native "*WebKitNamedFlow" {
 
 
 /// @domName WebSocket; @docsEditable true
+@SupportedBrowser(SupportedBrowser.CHROME)
+@SupportedBrowser(SupportedBrowser.FIREFOX)
+@SupportedBrowser(SupportedBrowser.IE, '10')
+@SupportedBrowser(SupportedBrowser.SAFARI)
 class WebSocket extends EventTarget native "*WebSocket" {
 
   ///@docsEditable true
   factory WebSocket(String url) => WebSocket._create(url);
   static WebSocket _create(String url) => JS('WebSocket', 'new WebSocket(#)', url);
 
+  /**
+   * Checks if this type is supported on the current platform
+   */
+  static bool get supported => JS('bool', 'typeof window.WebSocket != "undefined"');
+
   /// @domName EventTarget.addEventListener, EventTarget.removeEventListener, EventTarget.dispatchEvent; @docsEditable true
   WebSocketEvents get on =>
     new WebSocketEvents(this);