Make Storage implement Map.

lib/dom/templates/html/interface/interface_Storage.darttemplate

Index: lib/dom/templates/html/interface/interface_Storage.darttemplate
diff --git a/lib/dom/templates/html/interface/interface_Storage.darttemplate b/lib/dom/templates/html/interface/interface_Storage.darttemplate
new file mode 100644
index 0000000000000000000000000000000000000000..d040370d560ed0d460bc3221fa007eb103e02cf6
--- /dev/null
+++ b/lib/dom/templates/html/interface/interface_Storage.darttemplate
@@ -0,0 +1,9 @@
+// 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.
+
+interface $ID extends Map<String, String> {
+/*
+$!MEMBERS
+*/
+}