Use a single ToplevelWindowEventHandler for the ash::Shell

ash/root_window_controller.h

Index: ash/root_window_controller.h
diff --git a/ash/root_window_controller.h b/ash/root_window_controller.h
index 3d6f2fd80435e911b503770ab051eaba510e714c..abe6ab99428c08ed4f890ba5498e395180237a67 100644
--- a/ash/root_window_controller.h
+++ b/ash/root_window_controller.h
@@ -42,6 +42,10 @@ namespace keyboard {
 class KeyboardController;
 }
 
+namespace ui {
+class EventHandler;
+}
+
 namespace ash {
 class ShelfWidget;
 class SoloWindowTracker;
@@ -302,13 +306,8 @@ class ASH_EXPORT RootWindowController : public ShellObserver {
   TouchHudDebug* touch_hud_debug_;
   TouchHudProjection* touch_hud_projection_;
 
-  // We need to own event handlers for various containers.
-  scoped_ptr<ToplevelWindowEventHandler> default_container_handler_;
-  scoped_ptr<ToplevelWindowEventHandler> always_on_top_container_handler_;
-  scoped_ptr<ToplevelWindowEventHandler> modal_container_handler_;
-  scoped_ptr<ToplevelWindowEventHandler> lock_modal_container_handler_;
-  scoped_ptr<ToplevelWindowEventHandler> panel_container_handler_;
-  scoped_ptr<ToplevelWindowEventHandler> docked_container_handler_;
+  // Handles double clicks on the panel window header.
+  scoped_ptr<ui::EventHandler> panel_container_handler_;
 
   scoped_ptr<DesktopBackgroundWidgetController> wallpaper_controller_;
   scoped_ptr<AnimatingDesktopController> animating_wallpaper_controller_;