Add a new implementation of HashMap that uses JS objects for its (multiple) hash tables.

runtime/lib/collection_sources.gypi

Index: runtime/lib/collection_sources.gypi
diff --git a/runtime/lib/json_sources.gypi b/runtime/lib/collection_sources.gypi
similarity index 60%
copy from runtime/lib/json_sources.gypi
copy to runtime/lib/collection_sources.gypi
index 1622f7bf6d74c4b04b1df5dd2318a6dc1ef69338..0783b7d7d314bd4ea0ba4dbf9c61ab11cd67e3d1 100644
--- a/runtime/lib/json_sources.gypi
+++ b/runtime/lib/collection_sources.gypi
@@ -1,9 +1,9 @@
-# Copyright (c) 2013, the Dart project authors.  Please see the AUTHORS file
+ # Copyright (c) 2013, 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.
 
 {
   'sources': [
-    'json_patch.dart',
+    'collection_patch.dart',
   ],
 }