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

sdk/lib/html/src/_Collections.dart

Index: sdk/lib/html/src/_Collections.dart
diff --git a/sdk/lib/html/src/_Collections.dart b/sdk/lib/html/src/_Collections.dart
index eb9749442b7e75d48ae99d268b9bac00ded98894..4bd77cd8e3453b32da11a7760c09f5a4cf8698ff 100644
--- a/sdk/lib/html/src/_Collections.dart
+++ b/sdk/lib/html/src/_Collections.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;
+
 /**
  * The [Collections] class implements static methods useful when
  * writing a class that implements [Collection] and the [iterator]