Adding missing 'part of html' statements.

sdk/lib/html/src/dart2js_DOMImplementation.dart

 // 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.
 
+part of html;
+
 // TODO(vsm): Unify with Dartium version.
 class _DOMWindowCrossFrame implements Window {
   // Private window.  Note, this is a window in another frame, so it
   // cannot be typed as "Window" as its prototype is not patched
   // properly.  Its fields and methods can only be accessed via JavaScript.
   var _window;
 
   // Fields.
   History get history =>
     _HistoryCrossFrame._createSafe(JS('History', '#.history', _window));
@@ skipping 79 matching lines @@
 
   static History _createSafe(h) {
     if (identical(h, window.history)) {
       return h;
     } else {
       // TODO(vsm): Cache or implement equality.
       return new _HistoryCrossFrame(h);
     }
   }
 }