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

third_party/WebKit/Source/devtools/front_end/elements/ElementStatePaneWidget.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.ElementStatePaneWidget = class extends UI.Widget {
   constructor() {
     super();
     this.element.className = 'styles-element-state-pane';
@@ skipping 90 matching lines @@
 };
 
 /**
  * @implements {UI.ToolbarItem.Provider}
  * @unrestricted
  */
 Elements.ElementStatePaneWidget.ButtonProvider = class {
   constructor() {
     this._button = new UI.ToolbarToggle(Common.UIString('Toggle Element State'), '');
     this._button.setText(Common.UIString(':hov'));
-    this._button.addEventListener(UI.ToolbarButton.Events.Click, this._clicked, this);
+    this._button.addEventListener('click', this._clicked, this);
     this._button.element.classList.add('monospace');
     this._view = new Elements.ElementStatePaneWidget();
   }
 
   _clicked() {
     Elements.ElementsPanel.instance().showToolbarPane(!this._view.isShowing() ? this._view : null, this._button);
   }
 
   /**
    * @override
    * @return {!UI.ToolbarItem}
    */
   item() {
     return this._button;
   }
 };