Enable tests related to the extensions web ui that were flaky.

chrome/browser/resources/extensions/extensions.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.
 
 <include src="../../../../ui/webui/resources/js/cr/ui/focus_row.js">
 <include src="../../../../ui/webui/resources/js/cr/ui/focus_grid.js">
 <include src="../uber/uber_utils.js">
 <include src="extension_code.js">
 <include src="extension_commands_overlay.js">
 <include src="extension_error_overlay.js">
@@ skipping 107 matching lines @@
 
     /**
      * True if drag-drop is both available and currently enabled - it can be
      * temporarily disabled while overlays are showing.
      * @type {boolean}
      * @private
      */
     dragEnabled_: false,
 
     /**
+     * Callback for testing purposes. This is called after the "Developer mode"
+     * checkbox is toggled and the div containing developer buttons' height has
+     * been set.
+     * @type {function()?}
+     */
+    testingDeveloperModeCallback: null,
+
+    /**
      * Perform initial setup.
      */
     initialize: function() {
       uber.onContentFrameLoaded();
       cr.ui.FocusOutlineManager.forDocument(document);
       measureCheckboxStrings();
 
       // Set the title.
       uber.setTitle(loadTimeData.getString('extensionSettings'));
 
@@ skipping 198 matching lines @@
       var buttons = devControls.querySelector('.button-container');
       Array.prototype.forEach.call(buttons.querySelectorAll('a, button'),
                                    function(control) {
         control.tabIndex = showDevControls ? 0 : -1;
       });
       buttons.setAttribute('aria-hidden', !showDevControls);
 
       window.requestAnimationFrame(function() {
         devControls.style.height = !showDevControls ? '' :
             buttons.offsetHeight + 'px';
+
+        if (this.testingDeveloperModeCallback)
+          this.testingDeveloperModeCallback();
       }.bind(this));
     },
 
     /** @override */
     onExtensionCountChanged: function() {
       /** @const */
       var hasExtensions = $('extension-settings-list').getNumExtensions() != 0;
       $('no-extensions').hidden = hasExtensions;
       $('extension-list-wrapper').hidden = !hasExtensions;
     },
@@ skipping 112 matching lines @@
   // Export
   return {
     ExtensionSettings: ExtensionSettings
   };
 });
 
 window.addEventListener('load', function(e) {
   document.documentElement.classList.add('loading');
   extensions.ExtensionSettings.getInstance().initialize();
 });