Add dummy dart:html library for documentation.

lib/html/doc/interface/IDBFactory.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 IDBFactory
+interface IDBFactory {
+
+  /** @domName IDBFactory.cmp */
+  int cmp(/*IDBKey*/ first, /*IDBKey*/ second);
+
+  /** @domName IDBFactory.deleteDatabase */
+  IDBVersionChangeRequest deleteDatabase(String name);
+
+  /** @domName IDBFactory.getDatabaseNames */
+  IDBRequest getDatabaseNames();
+
+  /** @domName IDBFactory.open */
+  IDBRequest open(String name);
+}