Add flag to enable immersive fullscreen for v2 apps

ash/wm/window_state_delegate.h

 // Copyright 2013 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 ASH_WM_WINDOW_STATE_DELEGATE_H_
 #define ASH_WM_WINDOW_STATE_DELEGATE_H_
 
 #include "ash/ash_export.h"
 #include "base/basictypes.h"
 
 namespace ash {
 namespace wm {
 class WindowState;
 
 class ASH_EXPORT WindowStateDelegate {
  public:
   WindowStateDelegate();
   virtual ~WindowStateDelegate();
 
-  // Invoked when the user uses Shift+F4/F4 to toggle the window
-  // fullscreen state.  The caller (ash::wm::WindowState) falls backs
-  // to the default implementation if this returns false.
+  // Invoked when the user uses Shift+F4/F4 to toggle the window fullscreen
+  // state. If the window is not fullscreen and the window supports immersive
+  // fullscreen ToggleFullscreen() should put the window into immersive
+  // fullscreen instead of the default fullscreen type. The caller
+  // (ash::wm::WindowState) falls backs to the default implementation if this
+  // returns false.
   virtual bool ToggleFullscreen(WindowState* window_state);
 
  private:
   DISALLOW_COPY_AND_ASSIGN(WindowStateDelegate);
 };
 
 }  // namespace wm
 }  // namespace ash
 
 #endif  // ASH_WM_WINDOW_STATE_DELEGATE_H_