Moves transient window observer methods out of WindowObserver

ui/aura/window_observer.h

Index: ui/aura/window_observer.h
diff --git a/ui/aura/window_observer.h b/ui/aura/window_observer.h
index 9408ee831dddb83c66c675bca8e197b96ed9b4ef..bd909d879d7a7375ea786502bd5abcde43079159 100644
--- a/ui/aura/window_observer.h
+++ b/ui/aura/window_observer.h
@@ -103,12 +103,6 @@ class AURA_EXPORT WindowObserver {
   // Called when a Window is about to be removed from a RootWindow.
   virtual void OnWindowRemovingFromRootWindow(Window* window) {}
 
-  // Called when a transient child is added to |window|.
-  virtual void OnAddTransientChild(Window* window, Window* transient) {}
-
-  // Called when a transient child is removed from |window|.
-  virtual void OnRemoveTransientChild(Window* window, Window* transient) {}
-
  protected:
   virtual ~WindowObserver() {}
 };