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

ui/aura/test/event_generator.h

Index: ui/aura/test/event_generator.h
diff --git a/ui/aura/test/event_generator.h b/ui/aura/test/event_generator.h
index 5f93c5ca9eb99a9648889d3f2856d88aa8b2eac1..02659bb233bc7bfeea83a4c8a18ee09bab9d8b70 100644
--- a/ui/aura/test/event_generator.h
+++ b/ui/aura/test/event_generator.h
@@ -87,7 +87,7 @@ class EventGenerator {
  public:
   // Creates an EventGenerator with the mouse/touch location (0,0),
   // which uses the |root_window|'s coordinates.
-  explicit EventGenerator(RootWindow* root_window);
+  explicit EventGenerator(Window* root_window);
 
   // Create an EventGenerator with EventGeneratorDelegate,
   // which uses the coordinates used by |delegate|.
@@ -95,11 +95,11 @@ class EventGenerator {
 
   // Creates an EventGenerator with the mouse/touch location
   // at |initial_location|, which uses the |root_window|'s coordinates.
-  EventGenerator(RootWindow* root_window, const gfx::Point& initial_location);
+  EventGenerator(Window* root_window, const gfx::Point& initial_location);
 
   // Creates an EventGenerator with the mouse/touch location
   // centered over |window|, which uses the |root_window|'s coordinates.
-  EventGenerator(RootWindow* root_window, Window* window);
+  EventGenerator(Window* root_window, Window* window);
 
   virtual ~EventGenerator();