DevTools: Introduce Landing page for Timeline 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 437 matching lines @@
     if (effectiveTab && this._autoSelectFirstItemOnShow)
       this.selectTab(effectiveTab.id);
   }
 
   /**
    * @param {boolean} enable
    */
   setTabSlider(enable) {
     this._sliderEnabled = enable;
     this._tabSlider.classList.toggle('enabled', enable);
+    this._headerElement.classList.add('tabbed-pane-no-tab-borders');
   }
 
   /**
    * @override
    * @return {!Constraints}
    */
   calculateConstraints() {
     var constraints = super.calculateConstraints();
     var minContentConstraints = new Constraints(new Size(0, 0), new Size(50, 50));
     constraints = constraints.widthToMax(minContentConstraints).heightToMax(minContentConstraints);
@@ skipping 741 matching lines @@
    * @param {!Array.<string>} ids
    */
   closeTabs(tabbedPane, ids) {},
 
   /**
    * @param {string} tabId
    * @param {!UI.ContextMenu} contextMenu
    */
   onContextMenu(tabId, contextMenu) {}
 };