[Extensions] Add logic for when to show the toolbar redesign bubble.

chrome/browser/ui/toolbar/toolbar_actions_bar_bubble_delegate.h

 // Copyright 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.
 
 #ifndef CHROME_BROWSER_UI_TOOLBAR_TOOLBAR_ACTIONS_BAR_BUBBLE_DELEGATE_H_
 #define CHROME_BROWSER_UI_TOOLBAR_TOOLBAR_ACTIONS_BAR_BUBBLE_DELEGATE_H_
 
 // A delegate for the toolbar actions bar bubble, which briefly tells users
 // about the toolbar redesign.
 class ToolbarActionsBarBubbleDelegate {
  public:
   enum CloseAction {
     ACKNOWLEDGED,
     DISMISSED,
   };
 
+  virtual void OnToolbarActionsBarBubbleShown() = 0;
   virtual void OnToolbarActionsBarBubbleClosed(CloseAction action) = 0;
 };
 
 #endif  // CHROME_BROWSER_UI_TOOLBAR_TOOLBAR_ACTIONS_BAR_BUBBLE_DELEGATE_H_