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

ash/test/mirror_window_test_api.h

Index: ash/test/mirror_window_test_api.h
diff --git a/ash/test/mirror_window_test_api.h b/ash/test/mirror_window_test_api.h
index bef8a9fb395a0cfcdae2a0081106c4475837948c..c18c2a71d3fcabe3923b86f2df60e99ddf4dc101 100644
--- a/ash/test/mirror_window_test_api.h
+++ b/ash/test/mirror_window_test_api.h
@@ -9,7 +9,6 @@
 #include "base/memory/scoped_ptr.h"
 
 namespace aura {
-class RootWindowTransformer;
 class Window;
 class WindowTreeHost;
 }
@@ -19,6 +18,8 @@ class Point;
 }
 
 namespace ash {
+class RootWindowTransformer;
+
 namespace test {
 
 class MirrorWindowTestApi {
@@ -32,7 +33,7 @@ class MirrorWindowTestApi {
   const gfx::Point& GetCursorHotPoint() const;
   const aura::Window* GetCursorWindow() const;
 
-  scoped_ptr<aura::RootWindowTransformer>
+  scoped_ptr<RootWindowTransformer>
       CreateCurrentRootWindowTransformer() const;
 
  private: