Fix the full screen switching browser window dipping below launcher bar issue.

ui/aura/root_window_observer.h

 // Copyright (c) 2012 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 UI_AURA_ROOT_WINDOW_OBSERVER_H_
 #define UI_AURA_ROOT_WINDOW_OBSERVER_H_
 #pragma once
 
 #include "ui/aura/aura_export.h"
 
 namespace gfx {
 class Size;
 }
 
 namespace aura {
 
 class Window;
 
 class AURA_EXPORT RootWindowObserver {
  public:
   // Invoked after the RootWindow is resized.
   virtual void OnRootWindowResized(const gfx::Size& new_size) {}
 
+  // Invoked after the screen's work area insets changes.
+  virtual void OnScreenWorkAreaInsetsChanged() {}
+
   // Invoked when a window is focused.
   virtual void OnWindowFocused(Window* window) {}
 
  protected:
   virtual ~RootWindowObserver() {}
 };
 
 }  // namespace aura
 
 #endif  // UI_AURA_ROOT_WINDOW_OBSERVER_H_