Second attempt at moving the StackingClient to a property on the RootWindow.

ui/aura/root_window.h

Index: ui/aura/root_window.h
===================================================================
--- ui/aura/root_window.h	(revision 114527)
+++ ui/aura/root_window.h	(working copy)
@@ -37,7 +37,6 @@
 class KeyEvent;
 class MouseEvent;
 class ScreenAura;
-class StackingClient;
 class TouchEvent;
 
 // RootWindow is responsible for hosting a set of windows.
@@ -56,13 +55,10 @@
   ui::Compositor* compositor() { return compositor_.get(); }
   gfx::Point last_mouse_location() const { return last_mouse_location_; }
   gfx::NativeCursor last_cursor() const { return last_cursor_; }
-  StackingClient* stacking_client() { return stacking_client_.get(); }
   Window* mouse_pressed_handler() { return mouse_pressed_handler_; }
   Window* capture_window() { return capture_window_; }
   ScreenAura* screen() { return screen_; }
 
-  void SetStackingClient(StackingClient* stacking_client);
-
   // Shows the root window host.
   void ShowRootWindow();
 
@@ -181,8 +177,6 @@
 
   scoped_ptr<RootWindowHost> host_;
 
-  scoped_ptr<StackingClient> stacking_client_;
-
   static RootWindow* instance_;
 
   // If set before the RootWindow is created, the host window will cover the