Add a full screen virtual keyboard to virtual keyboard root window

ash/display/virtual_keyboard_window_controller.h

Index: ash/display/virtual_keyboard_window_controller.h
diff --git a/ash/display/virtual_keyboard_window_controller.h b/ash/display/virtual_keyboard_window_controller.h
index def3c06fc99814944a0f206134a41d397e74a28f..9d59feb6c1063bec0570716f90097b7ef595fc85 100644
--- a/ash/display/virtual_keyboard_window_controller.h
+++ b/ash/display/virtual_keyboard_window_controller.h
@@ -22,6 +22,10 @@ class ASH_EXPORT VirtualKeyboardWindowController {
   VirtualKeyboardWindowController();
   virtual ~VirtualKeyboardWindowController();
 
+  RootWindowController* root_window_controller() {
+    return root_window_controller_.get();
+  }
+
   // Updates the root window's bounds using |display_info|.
   // Creates the new root window if one doesn't exist.
   void UpdateWindow(const DisplayInfo& display_info);