Add dummy dart:html library for documentation.

lib/html/doc/interface/MediaController.dart

+// 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: Do not edit - generated code.
+
+/// @domName MediaController
+interface MediaController extends EventTarget default _MediaControllerFactoryProvider {
+
+  MediaController();
+
+  /** @domName MediaController.buffered */
+  final TimeRanges buffered;
+
+  /** @domName MediaController.currentTime */
+  num currentTime;
+
+  /** @domName MediaController.defaultPlaybackRate */
+  num defaultPlaybackRate;
+
+  /** @domName MediaController.duration */
+  final num duration;
+
+  /** @domName MediaController.muted */
+  bool muted;
+
+  /** @domName MediaController.paused */
+  final bool paused;
+
+  /** @domName MediaController.playbackRate */
+  num playbackRate;
+
+  /** @domName MediaController.played */
+  final TimeRanges played;
+
+  /** @domName MediaController.seekable */
+  final TimeRanges seekable;
+
+  /** @domName MediaController.volume */
+  num volume;
+
+  /** @domName MediaController.addEventListener */
+  void $dom_addEventListener(String type, EventListener listener, [bool useCapture]);
+
+  /** @domName MediaController.dispatchEvent */
+  bool $dom_dispatchEvent(Event evt);
+
+  /** @domName MediaController.pause */
+  void pause();
+
+  /** @domName MediaController.play */
+  void play();
+
+  /** @domName MediaController.removeEventListener */
+  void $dom_removeEventListener(String type, EventListener listener, [bool useCapture]);
+}