Introdcue AshWindowTreeHost and move ash/chrome specific code in WTH to ash.

ash/display/mirror_window_controller.h

Index: ash/display/mirror_window_controller.h
diff --git a/ash/display/mirror_window_controller.h b/ash/display/mirror_window_controller.h
index c70e9d8a211897ebd2f17012c5c19a2c45997926..8765c87ae6bad3c79d69ee80a4a11ce5ebd5d462 100644
--- a/ash/display/mirror_window_controller.h
+++ b/ash/display/mirror_window_controller.h
@@ -9,7 +9,6 @@
 #include "base/compiler_specific.h"
 #include "base/memory/ref_counted.h"
 #include "base/memory/scoped_ptr.h"
-#include "ui/aura/window_tree_host.h"
 #include "ui/aura/window_tree_host_observer.h"
 #include "ui/gfx/display.h"
 #include "ui/gfx/native_widget_types.h"
@@ -17,7 +16,6 @@
 #include "ui/gfx/size.h"
 
 namespace aura {
-class RootWindowTransformer;
 class Window;
 }
 
@@ -26,6 +24,8 @@ class Reflector;
 }
 
 namespace ash {
+class AshWindowTreeHost;
+class RootWindowTransformer;
 namespace test{
 class MirrorWindowTestApi;
 }
@@ -55,16 +55,16 @@ class ASH_EXPORT MirrorWindowController : public aura::WindowTreeHostObserver {
   // aura::WindowTreeHostObserver overrides:
   virtual void OnHostResized(const aura::WindowTreeHost* host) OVERRIDE;
 
-  aura::WindowTreeHost* host() const { return host_.get(); }
+  AshWindowTreeHost* ash_host() const { return ash_host_.get(); }
 
  private:
   friend class test::MirrorWindowTestApi;
 
   // Creates a RootWindowTransformer for current display
   // configuration.
-  scoped_ptr<aura::RootWindowTransformer> CreateRootWindowTransformer() const;
+  scoped_ptr<RootWindowTransformer> CreateRootWindowTransformer() const;
 
-  scoped_ptr<aura::WindowTreeHost> host_;
+  scoped_ptr<AshWindowTreeHost> ash_host_;
   gfx::Size mirror_window_host_size_;
   scoped_refptr<ui::Reflector> reflector_;