bluetooth: Fix flaky bluetooth internals browser test.

chrome/browser/resources/bluetooth_internals/snackbar.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.
 
 /**
  * Javascript for Snackbar controls, served from chrome://bluetooth-internals/.
  */
 
 cr.define('snackbar', function() {
   /** @typedef {{
    *    message: string,
    *    type: string,
    *    actionText: (string|undefined),
    *    action: (function()|undefined)
    *  }}
    */
   var SnackbarOptions;
 
   /** @const {number} */ var SHOW_DURATION = 5000;
+  /** @const {number} */ var TRANSITION_DURATION = 225;
 
   /**
    * Enum of Snackbar types. Used by Snackbar to determine the styling for the
    * Snackbar.
    * @enum {string}
    */
   var SnackbarType = {
     INFO: 'info',
     SUCCESS: 'success',
     WARNING: 'warning',
@@ skipping 40 matching lines @@
       this.classList.add(options.type);
       this.actionLink_.textContent = options.actionText || 'Dismiss';
 
       this.actionLink_.addEventListener('click', function() {
         if (options.action) options.action();
         this.dismiss();
       }.bind(this));
     },
 
     /**
-     * Shows the Snackbar.
+     * Shows the Snackbar and dispatches the 'showed' event.
      */
     show: function() {
       this.classList.add('open');
       if (Snackbar.hasContentFocus_) this.startTimeout_();
       else this.stopTimeout_();
 
       document.addEventListener('contentfocus', this.boundStartTimeout_);
       document.addEventListener('contentblur', this.boundStopTimeout_);
+      this.dispatchEvent(new CustomEvent('showed'));
     },
 
     /**
      * Dismisses the Snackbar. Once the Snackbar is completely hidden, the
-     * 'dismissed' event is fired.
+     * 'dismissed' event is fired and the returned Promise is resolved. If the
+     * snackbar is already hidden, a resolved Promise is returned.
+     * @return {!Promise}
      */
     dismiss: function() {
-      this.addEventListener('webkitTransitionEnd', function(event) {
-        if (event.propertyName === 'transform')
+      this.stopTimeout_();
+
+      if (!this.classList.contains('open'))
+        return Promise.resolve();
+
+      return new Promise(function(resolve) {
+        listenOnce(this, 'webkitTransitionEnd', function() {
           this.dispatchEvent(new CustomEvent('dismissed'));
+          resolve();
+        }.bind(this));
+
+        ensureTransitionEndEvent(this, TRANSITION_DURATION);
+        this.classList.remove('open');
+
+        document.removeEventListener('contentfocus', this.boundStartTimeout_);
+        document.removeEventListener('contentblur', this.boundStopTimeout_);
       }.bind(this));
-
-      ensureTransitionEndEvent(this, SHOW_DURATION);
-      this.classList.remove('open');
-
-      document.removeEventListener('contentfocus', this.boundStartTimeout_);
-      document.removeEventListener('contentblur', this.boundStopTimeout_);
     },
 
     /**
      * Starts the timeout for dismissing the Snackbar.
      * @private
      */
     startTimeout_: function() {
       this.timeoutId_ = setTimeout(function() {
         this.dismiss();
       }.bind(this), SHOW_DURATION);
@@ skipping 91 matching lines @@
     }, 10);
   };
 
   /**
    * Dismisses the Snackbar currently showing.
    * @param {boolean} clearQueue If true, clears the Snackbar queue before
    *     dismissing.
    */
   Snackbar.dismiss = function(clearQueue) {
     if (clearQueue) Snackbar.queue_ = [];
-    if (Snackbar.current_) Snackbar.current_.dismiss();
+    if (Snackbar.current_) return Snackbar.current_.dismiss();
+    return Promise.resolve();
   };
 
 
 
   return {
     Snackbar: Snackbar,
     SnackbarType: SnackbarType,
   };
 });