Make GetRootWindow() return a Window instead of a RootWindow.

ui/aura/window.h

Index: ui/aura/window.h
diff --git a/ui/aura/window.h b/ui/aura/window.h
index e908de4b470d6b54daf0e7b22b7a1c5cd1ca6d5c..e11f83acf5b507ef1d515770bf41b6e4564ea9f1 100644
--- a/ui/aura/window.h
+++ b/ui/aura/window.h
@@ -46,6 +46,9 @@ class RootWindow;
 class WindowDelegate;
 class WindowObserver;
 
+// TODO(beng): remove once RootWindow is renamed.
+typedef RootWindow WindowEventDispatcher;
+
 // Defined in window_property.h (which we do not include)
 template<typename T>
 struct WindowProperty;
@@ -108,10 +111,19 @@ class AURA_EXPORT Window : public ui::LayerDelegate,
   Window* parent() { return parent_; }
   const Window* parent() const { return parent_; }
 
-  // Returns the RootWindow that contains this Window or NULL if the Window is
-  // not contained by a RootWindow.
-  virtual RootWindow* GetRootWindow();
-  virtual const RootWindow* GetRootWindow() const;
+  // Returns the root Window that contains this Window. The root Window is
+  // defined as the Window that has a dispatcher. These functions return NULL if
+  // the Window is contained in a hierarchy that does not have a dispatcher at
+  // its root.
+  virtual Window* GetRootWindow();
+  virtual const Window* GetRootWindow() const;
+
+  WindowEventDispatcher* GetDispatcher();
+  const WindowEventDispatcher* GetDispatcher() const;
+  void set_dispatcher(WindowEventDispatcher* dispatcher) {
+    dispatcher_ = dispatcher;
+  }
+  bool HasDispatcher() const { return !!dispatcher_; }
 
   // The Window does not own this object.
   void set_user_data(void* user_data) { user_data_ = user_data; }
@@ -475,6 +487,8 @@ class AURA_EXPORT Window : public ui::LayerDelegate,
   // Returns true if the mouse is currently within our bounds.
   bool ContainsMouse();
 
+  WindowEventDispatcher* dispatcher_;
+
   client::WindowType type_;
 
   // True if the Window is owned by its parent - i.e. it will be deleted by its