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

sdk/lib/html/src/Timer.dart

Index: sdk/lib/html/src/Timer.dart
diff --git a/sdk/lib/html/src/Timer.dart b/sdk/lib/html/src/Timer.dart
index 35ceac29da66e27906a68d565814e2c0909340ce..91ad28118c1d4cdf6f4308a7e0ad06ecf2317648 100644
--- a/sdk/lib/html/src/Timer.dart
+++ b/sdk/lib/html/src/Timer.dart
@@ -2,6 +2,8 @@
 // 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;