Rename RootWindowHost* to WindowTreeHost*

ash/shell.h

Index: ash/shell.h
diff --git a/ash/shell.h b/ash/shell.h
index 31933066f4c94dab8c4a55da54109fddc1892ae5..a452cd53ea473bf7e5d54b8df26ecba669c4cc16 100644
--- a/ash/shell.h
+++ b/ash/shell.h
@@ -92,7 +92,7 @@ class NestedDispatcherController;
 class NewWindowDelegate;
 class PartialMagnificationController;
 class PowerButtonController;
-class RootWindowHostFactory;
+class WindowTreeHostFactory;
 class ScreenAsh;
 class SessionStateDelegate;
 class Shelf;
@@ -500,7 +500,7 @@ class ASH_EXPORT Shell
     return resolution_notification_controller_.get();
   }
 
-  RootWindowHostFactory* root_window_host_factory() {
+  WindowTreeHostFactory* root_window_host_factory() {
     return root_window_host_factory_.get();
   }
 
@@ -644,7 +644,7 @@ class ASH_EXPORT Shell
   scoped_ptr<internal::EventClientImpl> event_client_;
   scoped_ptr<internal::EventTransformationHandler>
       event_transformation_handler_;
-  scoped_ptr<RootWindowHostFactory> root_window_host_factory_;
+  scoped_ptr<WindowTreeHostFactory> root_window_host_factory_;
 
   // An event filter that rewrites or drops an event.
   scoped_ptr<internal::EventRewriterEventFilter> event_rewriter_filter_;