[MD History] Add UMA stats for switching views and the CBD button.

chrome/test/data/webui/md_history/test_util.js

 // Copyright 2016 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.
 
 /*
  * Waits for queued up tasks to finish before proceeding. Inspired by:
  * https://github.com/Polymer/web-component-tester/blob/master/browser/environment/helpers.js#L97
  */
 function flush() {
   Polymer.dom.flush();
@@ skipping 93 matching lines @@
 
       resolve();
       element.removeEventListener(eventName, listener);
     }
 
     element.addEventListener(eventName, listener);
   });
 }
 
 /**
+ * @return {Promise}
+ */
+function waitForAnimationFrame() {
+  return new Promise(function(resolve) {
+    requestAnimationFrame(function() { setTimeout(resolve); });
+  });
+}
+
+/**
  * Sends a shift click event to |element|.
  * @param {HTMLElement} element
  */
 function shiftClick(element) {
   var xy = MockInteractions.middleOfNode(element);
   var props = {
     bubbles: true,
     cancelable: true,
     clientX: xy.x,
     clientY: xy.y,
     buttons: 1,
     shiftKey: true,
   };
 
   element.dispatchEvent(new MouseEvent('mousedown', props));
   element.dispatchEvent(new MouseEvent('mouseup', props));
   element.dispatchEvent(new MouseEvent('click', props));
 }