Add dummy dart:html library for documentation.

lib/html/doc/interface/WorkerLocation.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 WorkerLocation
+interface WorkerLocation {
+
+  /** @domName WorkerLocation.hash */
+  final String hash;
+
+  /** @domName WorkerLocation.host */
+  final String host;
+
+  /** @domName WorkerLocation.hostname */
+  final String hostname;
+
+  /** @domName WorkerLocation.href */
+  final String href;
+
+  /** @domName WorkerLocation.pathname */
+  final String pathname;
+
+  /** @domName WorkerLocation.port */
+  final String port;
+
+  /** @domName WorkerLocation.protocol */
+  final String protocol;
+
+  /** @domName WorkerLocation.search */
+  final String search;
+
+  /** @domName WorkerLocation.toString */
+  String toString();
+}