Rename RootWindowHost* to WindowTreeHost*

ui/aura/root_window_observer.h

Index: ui/aura/root_window_observer.h
diff --git a/ui/aura/root_window_observer.h b/ui/aura/root_window_observer.h
index bfb8e65c518a6a7ddd434bba919eabf6cabd0ac8..0ef86e127e8dd11843a6dc177b9dcb766c277862 100644
--- a/ui/aura/root_window_observer.h
+++ b/ui/aura/root_window_observer.h
@@ -19,15 +19,15 @@ class Window;
 class AURA_EXPORT RootWindowObserver {
  public:
   // Invoked after the RootWindow's host has been resized.
-  virtual void OnRootWindowHostResized(const RootWindow* root) {}
+  virtual void OnWindowTreeHostResized(const RootWindow* root) {}
 
   // Invoked after the RootWindow's host has been moved on screen.
-  virtual void OnRootWindowHostMoved(const RootWindow* root,
+  virtual void OnWindowTreeHostMoved(const RootWindow* root,
                                      const gfx::Point& new_origin) {}
 
   // Invoked when the native windowing system sends us a request to close our
   // window.
-  virtual void OnRootWindowHostCloseRequested(const RootWindow* root) {}
+  virtual void OnWindowTreeHostCloseRequested(const RootWindow* root) {}
 
   // Invoked when the keyboard mapping has changed.
   virtual void OnKeyboardMappingChanged(const RootWindow* root) {}