Make win_aura work without ash.

ui/aura/root_window_host.h

Index: ui/aura/root_window_host.h
===================================================================
--- ui/aura/root_window_host.h	(revision 134107)
+++ ui/aura/root_window_host.h	(working copy)
@@ -34,9 +34,15 @@
   // (gfx::Screen only reports on the virtual desktop exposed by Aura.)
   static gfx::Size GetNativeScreenSize();
 
+  // Returns the RootWindowHost for the specified accelerated widget, or NULL if
+  // there is none associated.
+  static RootWindowHost* GetForAcceleratedWidget(
+      gfx::AcceleratedWidget accelerated_widget);
+
   // Sets the RootWindow this RootWindowHost is hosting. RootWindowHost does not
   // own the RootWindow.
   virtual void SetRootWindow(RootWindow* root_window) = 0;
+  virtual RootWindow* GetRootWindow() = 0;
 
   // Returns the accelerated widget.
   virtual gfx::AcceleratedWidget GetAcceleratedWidget() = 0;