Add flag to enable immersive fullscreen for v2 apps

ash/wm/caption_buttons/frame_caption_button_container_view.h

Index: ash/wm/caption_buttons/frame_caption_button_container_view.h
diff --git a/ash/wm/caption_buttons/frame_caption_button_container_view.h b/ash/wm/caption_buttons/frame_caption_button_container_view.h
index bcd5b376fe323ccaf686b563e6ed11c3d7f3a242..3b88cbc095f3d1167726ab672abd068d32f20eed 100644
--- a/ash/wm/caption_buttons/frame_caption_button_container_view.h
+++ b/ash/wm/caption_buttons/frame_caption_button_container_view.h
@@ -16,6 +16,7 @@ class Widget;
 }
 
 namespace ash {
+class FrameMaximizeButton;
 
 // Container view for the frame caption buttons. It performs the appropriate
 // action when a caption button is clicked.
@@ -76,6 +77,10 @@ class ASH_EXPORT FrameCaptionButtonContainerView
     DISALLOW_COPY_AND_ASSIGN(TestApi);
   };
 
+  // Returns the size button if using the old caption button style, returns NULL
+  // otherwise.
+  FrameMaximizeButton* GetOldStyleSizeButton();
+
   // Tell the window controls to reset themselves to the normal state.
   void ResetWindowControls();