[Media Router] Animate transition between sink list and filter views.

chrome/browser/resources/media_router/externs.js

 // Copyright 2015 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.
 
 /**
  * @fileoverview Externs to be declared to properly compile JS code.
  * @externs
  */
 
 var performance = {};
 
 /**
  * @return {number}
  */
 performance.now = function() {};
 
 /** @interface */
 var InputDeviceCapabilities;
 
 /** @type {?InputDeviceCapabilities} */
 Event.prototype.sourceCapabilities;
+
+/**
+ * @interface
+ */
+var AnimationEffect = function() {};
+
+/**
+ * @param {Element} target
+ * @param {!Array<!Object>} frames
+ * @param {(number|Object)=} timing
+ * @constructor
+ * @implements {AnimationEffect}
+ */
+var KeyframeEffect = function(target, frames, timing) {};
+
+/**
+ * @param {!Array<!AnimationEffect>} group
+ * @constructor
+ * @implements {AnimationEffect}
+ */
+var GroupEffect = function(group) {};
+
+/**
+ * @interface
+ */
+var Animation = function() {};
+
+/**
+ * @return {undefined}
+ */
+Animation.prototype.cancel = function() {};
+
+/**
+ * @type {!Promise}
+ */
+Animation.prototype.finished;
+
+document.timeline = {};
+
+/**
+ * @param {!AnimationEffect} effect
+ * @return {!Animation}
+ */
+document.timeline.play = function(effect) {};