Add dummy dart:html library for documentation.

lib/html/doc/interface/StorageEvent.dartdoc

+// 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.
+
+// WARNING:
+//   This file contains documentation that is merged into the real source.
+//   Do not make code changes here.
+
+/// @domName StorageEvent
+interface StorageEvent extends Event {
+
+  /** @domName StorageEvent.key */
+  final String key;
+
+  /** @domName StorageEvent.newValue */
+  final String newValue;
+
+  /** @domName StorageEvent.oldValue */
+  final String oldValue;
+
+  /** @domName StorageEvent.storageArea */
+  final Storage storageArea;
+
+  /** @domName StorageEvent.url */
+  final String url;
+
+  /** @domName StorageEvent.initStorageEvent */
+  void initStorageEvent(String typeArg, bool canBubbleArg, bool cancelableArg, String keyArg, String oldValueArg, String newValueArg, String urlArg, Storage storageAreaArg);
+}