[DevTools] Fix popover regression in M58

third_party/WebKit/Source/devtools/front_end/ui/Popover.js

 /*
  * Copyright (C) 2009 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 18 matching lines @@
  */
 
 /**
  * @unrestricted
  */
 UI.Popover = class extends UI.Widget {
   /**
    * @param {!UI.PopoverHelper=} popoverHelper
    */
   constructor(popoverHelper) {
-    super(true);
+    super(false);
     this.markAsRoot();
+    this.element.classList.add('popover-element');
     this.registerRequiredCSS('ui/popover.css');
     this._containerElement = createElementWithClass('div', 'fill popover-container');
     this._popupArrowElement = this.contentElement.createChild('div', 'arrow');
     this._contentDiv = this.contentElement.createChild('div', 'popover-content');
     this._popoverHelper = popoverHelper;
     this._hideBound = this.hide.bind(this);
   }
 
   /**
    * @param {!Element} element
@@ skipping 324 matching lines @@
     if (this._hidePopoverTimer) {
       clearTimeout(this._hidePopoverTimer);
       delete this._hidePopoverTimer;
 
       // We know that we reached the popup, but we might have moved over other elements.
       // Discard pending command.
       this._resetHoverTimer();
     }
   }
 };