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

ash/display/root_window_transformers.h

Index: ash/display/root_window_transformers.h
diff --git a/ash/display/root_window_transformers.h b/ash/display/root_window_transformers.h
index e1d405333434a067c43b6303cfc22c54b72f2ae3..4a6e18c9707e00fd8557f240461a48a666253683 100644
--- a/ash/display/root_window_transformers.h
+++ b/ash/display/root_window_transformers.h
@@ -8,7 +8,6 @@
 #include "ash/ash_export.h"
 
 namespace aura {
-class RootWindowTransformer;
 class Window;
 }
 
@@ -18,10 +17,11 @@ class Transform;
 }
 
 namespace ash {
+class RootWindowTransformer;
 namespace internal {
 class DisplayInfo;
 
-ASH_EXPORT aura::RootWindowTransformer* CreateRootWindowTransformerForDisplay(
+ASH_EXPORT RootWindowTransformer* CreateRootWindowTransformerForDisplay(
     aura::Window* root,
     const gfx::Display& display);
 
@@ -29,7 +29,7 @@ ASH_EXPORT aura::RootWindowTransformer* CreateRootWindowTransformerForDisplay(
 // |source_display_info| specifies the display being mirrored,
 // and |mirror_display_info| specifies the display used to
 // mirror the content.
-ASH_EXPORT aura::RootWindowTransformer*
+ASH_EXPORT RootWindowTransformer*
 CreateRootWindowTransformerForMirroredDisplay(
     const DisplayInfo& source_display_info,
     const DisplayInfo& mirror_display_info);