Add dummy dart:html library for documentation.

lib/html/doc/interface/AnchorElement.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 HTMLAnchorElement
+interface AnchorElement extends Element default _Elements {
+
+  AnchorElement([String href]);
+
+  /** @domName HTMLAnchorElement.charset */
+  String charset;
+
+  /** @domName HTMLAnchorElement.coords */
+  String coords;
+
+  /** @domName HTMLAnchorElement.download */
+  String download;
+
+  /** @domName HTMLAnchorElement.hash */
+  String hash;
+
+  /** @domName HTMLAnchorElement.host */
+  String host;
+
+  /** @domName HTMLAnchorElement.hostname */
+  String hostname;
+
+  /** @domName HTMLAnchorElement.href */
+  String href;
+
+  /** @domName HTMLAnchorElement.hreflang */
+  String hreflang;
+
+  /** @domName HTMLAnchorElement.name */
+  String name;
+
+  /** @domName HTMLAnchorElement.origin */
+  final String origin;
+
+  /** @domName HTMLAnchorElement.pathname */
+  String pathname;
+
+  /** @domName HTMLAnchorElement.ping */
+  String ping;
+
+  /** @domName HTMLAnchorElement.port */
+  String port;
+
+  /** @domName HTMLAnchorElement.protocol */
+  String protocol;
+
+  /** @domName HTMLAnchorElement.rel */
+  String rel;
+
+  /** @domName HTMLAnchorElement.rev */
+  String rev;
+
+  /** @domName HTMLAnchorElement.search */
+  String search;
+
+  /** @domName HTMLAnchorElement.shape */
+  String shape;
+
+  /** @domName HTMLAnchorElement.target */
+  String target;
+
+  /** @domName HTMLAnchorElement.type */
+  String type;
+
+  /** @domName HTMLAnchorElement.toString */
+  String toString();
+}