[Chromoting] Additional prototypes for jscompile.

remoting/webapp/js_proto/dom_proto.js

 // Copyright (c) 2012 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 // This file contains various hacks needed to inform JSCompiler of various
 // WebKit- and Chrome-specific properties and methods. It is used only with
 // JSCompiler to verify the type-correctness of our code.
 
 /** @type {HTMLElement} */
 Document.prototype.activeElement;
@@ skipping 211 matching lines @@
  */
 Promise.reject = function (reason) {};
 
 /**
  * @param {*=} value
  * @return {Promise}
  */
 Promise.resolve = function (value) {};
 
 /**
+ * @type {DataTransfer}
+ */
+Event.prototype.dataTransfer = null;
+
+/**
  * @param {string} type
  * @param {boolean} canBubble
  * @param {boolean} cancelable
  * @param {Window} view
  * @param {number} detail
  * @param {number} screenX
  * @param {number} screenY
  * @param {number} clientX
  * @param {number} clientY
  * @param {boolean} ctrlKey
  * @param {boolean} altKey
  * @param {boolean} shiftKey
  * @param {boolean} metaKey
  * @param {number} button
  * @param {EventTarget} relatedTarget
  */
 Event.prototype.initMouseEvent = function(
     type, canBubble, cancelable, view, detail,
     screenX, screenY, clientX, clientY,
     ctrlKey, altKey, shiftKey, metaKey,
     button, relatedTarget) {};
 
 /**
  * @param {number} begin
  * @param {number=} end
  * @return {ArrayBuffer}
  */
 ArrayBuffer.prototype.slice = function(begin, end) {};