Revert of [DevTools] Remove methods on Common.Event.

third_party/WebKit/Source/devtools/front_end/elements/ClassesPaneWidget.js

 // Copyright (c) 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.
 /**
  * @unrestricted
  */
 Elements.ClassesPaneWidget = class extends UI.Widget {
   constructor() {
     super();
     this.element.className = 'styles-element-classes-pane';
@@ skipping 166 matching lines @@
 
 /**
  * @implements {UI.ToolbarItem.Provider}
  * @unrestricted
  */
 Elements.ClassesPaneWidget.ButtonProvider = class {
   constructor() {
     this._button = new UI.ToolbarToggle(Common.UIString('Element Classes'), '');
     this._button.setText('.cls');
     this._button.element.classList.add('monospace');
-    this._button.addEventListener(UI.ToolbarButton.Events.Click, this._clicked, this);
+    this._button.addEventListener('click', this._clicked, this);
     this._view = new Elements.ClassesPaneWidget();
   }
 
   _clicked() {
     Elements.ElementsPanel.instance().showToolbarPane(!this._view.isShowing() ? this._view : null, this._button);
   }
 
   /**
    * @override
    * @return {!UI.ToolbarItem}
@@ skipping 57 matching lines @@
     if (!this._classNamesPromise || this._selectedFrameId !== selectedNode.frameId())
       this._classNamesPromise = this._getClassNames(selectedNode);
 
     return this._classNamesPromise.then(completions => {
       if (prefix[0] === '.')
         completions = completions.map(value => '.' + value);
       return completions.filter(value => value.startsWith(prefix)).map(completion => ({title: completion}));
     });
   }
 };