Rename RootWindowHost* to WindowTreeHost*

ui/views/widget/widget.h

Index: ui/views/widget/widget.h
diff --git a/ui/views/widget/widget.h b/ui/views/widget/widget.h
index c27319226d0cdb27b88dfffb5587953678d01b5c..3e9831118623a88c9e7c51608ab0dd5af3f81ac1 100644
--- a/ui/views/widget/widget.h
+++ b/ui/views/widget/widget.h
@@ -52,7 +52,7 @@ class ThemeProvider;
 
 namespace views {
 
-class DesktopRootWindowHost;
+class DesktopWindowTreeHost;
 class InputMethod;
 class NativeWidget;
 class NonClientFrameView;
@@ -205,11 +205,11 @@ class VIEWS_EXPORT Widget : public internal::NativeWidgetDelegate,
     // When set, this value is used as the Widget's NativeWidget implementation.
     // The Widget will not construct a default one. Default is NULL.
     NativeWidget* native_widget;
-    // Aura-only. Provides a DesktopRootWindowHost implementation to use instead
+    // Aura-only. Provides a DesktopWindowTreeHost implementation to use instead
     // of the default one.
     // TODO(beng): Figure out if there's a better way to expose this, e.g. get
     // rid of NW subclasses and do this all via message handling.
-    DesktopRootWindowHost* desktop_root_window_host;
+    DesktopWindowTreeHost* desktop_root_window_host;
     // Whether this window is intended to be a toplevel window with no
     // attachment to any other window. (This may be a transient window if
     // |parent| is set.)