Adding 'part of html' to all files which are used by dart:html.

sdk/lib/html/src/Timer.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(antonm): support not DOM isolates too.
 class _Timer implements Timer {
   final canceller;
 
   _Timer(this.canceller);
 
   void cancel() { canceller(); }
 }
 
 get _timerFactoryClosure => (int milliSeconds, void callback(Timer timer), bool repeating) {
   var maker;
   var canceller;
   if (repeating) {
     maker = window.setInterval;
     canceller = window.clearInterval;
   } else {
     maker = window.setTimeout;
     canceller = window.clearTimeout;
   }
   Timer timer;
   final int id = maker(() { callback(timer); }, milliSeconds);
   timer = new _Timer(() { canceller(id); });
   return timer;
 };