DevTools: do not add paint profiler tab more than once on Layers panel

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

 /*
  * Copyright (C) 2010 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 173 matching lines @@
    * @param {!UI.Widget} view
    * @param {string=} tabTooltip
    * @param {boolean=} userGesture
    * @param {boolean=} isCloseable
    * @param {number=} index
    */
   appendTab(id, tabTitle, view, tabTooltip, userGesture, isCloseable, index) {
     isCloseable = typeof isCloseable === 'boolean' ? isCloseable : this._closeableTabs;
     var tab = new UI.TabbedPaneTab(this, id, tabTitle, isCloseable, view, tabTooltip);
     tab.setDelegate(this._delegate);
+    console.assert(!this._tabsById[id], `Tabbed pane already contains a tab with id '${id}'`);
     this._tabsById[id] = tab;
     if (index !== undefined)
       this._tabs.splice(index, 0, tab);
     else
       this._tabs.push(tab);
     this._tabsHistory.push(tab);
     view.attach(this);
     if (this._tabsHistory[0] === tab && this.isShowing())
       this.selectTab(tab.id, userGesture);
     this._updateTabElements();
@@ skipping 1006 matching lines @@
    * @param {!Array.<string>} ids
    */
   closeTabs(tabbedPane, ids) {},
 
   /**
    * @param {string} tabId
    * @param {!UI.ContextMenu} contextMenu
    */
   onContextMenu(tabId, contextMenu) {}
 };