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

sdk/lib/html/src/_Testing.dart

Index: sdk/lib/html/src/_Testing.dart
diff --git a/sdk/lib/html/src/_Testing.dart b/sdk/lib/html/src/_Testing.dart
index 2917141237b3cd8463163da47a0a0510f11c4714..7b15688675ac9f271d07f51cdef35445a25276b7 100644
--- a/sdk/lib/html/src/_Testing.dart
+++ b/sdk/lib/html/src/_Testing.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(rnystrom): add a way to supress public classes from DartDoc output.
 // TODO(jacobr): we can remove this class now that we are using the $dom_
 // convention for deprecated methods rather than truly private methods.
@@ -16,4 +18,4 @@ class Testing {
     target.$dom_removeEventListener(type, listener, useCapture);
   }
 
-}
+}