[DevTools] Do not inherit ObjectPopoverHelper from PopoverHelper.

third_party/WebKit/Source/devtools/front_end/perf_ui/TimelineOverviewPane.js

 /*
  * Copyright (C) 2013 Google Inc. All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions are
  * met:
  *
  *     * Redistributions of source code must retain the above copyright
  * notice, this list of conditions and the following disclaimer.
  *     * Redistributions in binary form must reproduce the above
@@ skipping 58 matching lines @@
   /**
    * @param {!Element} element
    * @param {!Event} event
    * @return {!Element|!AnchorBox|undefined}
    */
   _getPopoverAnchor(element, event) {
     return this._cursorArea;
   }
 
   /**
-   * @param {!Element} anchor
+   * @param {!Element|!AnchorBox} anchor
    * @param {!UI.GlassPane} popover
    * @return {!Promise<boolean>}
    */
   _showPopover(anchor, popover) {
     return this._buildPopoverContents().then(maybeShowPopover.bind(this));
 
     /**
      * @this {PerfUI.TimelineOverviewPane}
      * @param {!DocumentFragment} fragment
      * @return {boolean}
@@ skipping 454 matching lines @@
    */
   onClick(event) {
     return false;
   }
 
   resetCanvas() {
     this._canvas.width = this.element.clientWidth * window.devicePixelRatio;
     this._canvas.height = this.element.clientHeight * window.devicePixelRatio;
   }
 };