Revert "Revert "Add cancelAnimationFrame""

lib/dom/templates/html/frog/impl_Window.darttemplate

 // 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.
 
 class $CLASSNAME$EXTENDS$IMPLEMENTS native "@*DOMWindow" {
 
   _DocumentImpl get document() native "return this.document;";
 
   Window get _top() native "return this.top;";
 
   // Override top to return secure wrapper.
   Window get top() => _DOMWindowCrossFrameImpl._createSafe(_top);
 
   void requestLayoutFrame(TimeoutHandler callback) {
     _addMeasurementFrameCallback(callback);
   }
 
   /** @domName DOMWindow.requestAnimationFrame */
-  int requestAnimationFrame(RequestAnimationFrameCallback callback) native '''
-    if (!window.requestAnimationFrame) {
-      window.requestAnimationFrame =
-          window.webkitRequestAnimationFrame ||
-          window.mozRequestAnimationFrame ||
-          window.msRequestAnimationFrame ||
-          window.oRequestAnimationFrame ||
-          function (callback) {
-            window.setTimeout(callback, 16 /* 16ms ~= 60fps */);
-          };
-    }
-    return window.requestAnimationFrame(callback);
+  int requestAnimationFrame(RequestAnimationFrameCallback callback) {
+    _ensureRequestAnimationFrame();
+    return _requestAnimationFrame(callback);
+  }
+
+  void cancelAnimationFrame(id) {
+    _ensureRequestAnimationFrame();
+    _cancelAnimationFrame(id);
+  }
+
+  int _requestAnimationFrame(RequestAnimationFrameCallback callback)
+      native 'requestAnimationFrame';
+
+  void _cancelAnimationFrame(int id)
+      native 'cancelAnimationFrame';
+
+  _ensureRequestAnimationFrame() native '''
+   if (this.requestAnimationFrame && this.cancelAnimationFrame) return;
+   var vendors = ['ms', 'moz', 'webkit', 'o'];
+   for (var i = 0; i < vendors.length && !this.requestAnimationFrame; ++i) {
+     this.requestAnimationFrame = this[vendors[i] + 'RequestAnimationFrame'];
+     this.cancelAnimationFrame =
+         this[vendors[i]+'CancelAnimationFrame'] ||
+         this[vendors[i]+'CancelRequestAnimationFrame'];
+   }
+   if (this.requestAnimationFrame && this.cancelAnimationFrame) return;
+   this.requestAnimationFrame = function(callback) {
+       return window.setTimeout(callback, 16 /* 16ms ~= 60fps */);
+   };
+   this.cancelAnimationFrame = function(id) { clearTimeout(id); }
 ''';
 
-  // Protect member 'requestAnimationFrame'.
-  _requestAnimationFrame() native 'requestAnimationFrame';
-
 $!MEMBERS
 }