Use a single ToplevelWindowEventHandler for the ash::Shell

ash/shell.h

Index: ash/shell.h
diff --git a/ash/shell.h b/ash/shell.h
index 5c49f6b8bbcd5a4746ca3a6165668f9621e2aa3a..ab30d08fa66383a230bc5fdb6ca28f9ec32419f1 100644
--- a/ash/shell.h
+++ b/ash/shell.h
@@ -85,7 +85,6 @@ class DisplayController;
 class FirstRunHelper;
 class HighContrastController;
 class Launcher;
-class ShelfDelegate;
 class LockStateController;
 class MagnificationController;
 class MediaDelegate;
@@ -97,6 +96,7 @@ class PowerButtonController;
 class RootWindowHostFactory;
 class ScreenAsh;
 class SessionStateDelegate;
+class ShelfDelegate;
 class ShelfItemDelegateManager;
 class ShelfModel;
 class ShellDelegate;
@@ -105,6 +105,7 @@ class StickyKeys;
 class SystemTray;
 class SystemTrayDelegate;
 class SystemTrayNotifier;
+class ToplevelWindowEventHandler;
 class UserActivityDetector;
 class UserWallpaperDelegate;
 class VideoDetector;
@@ -651,6 +652,9 @@ class ASH_EXPORT Shell
   // An event filter for logging keyboard-related metrics.
   scoped_ptr<internal::KeyboardUMAEventFilter> keyboard_metrics_filter_;
 
+  // An event filter which handles moving and resizing windows.
+  scoped_ptr<ToplevelWindowEventHandler> toplevel_window_event_handler_;
+
   // An event filter which handles system level gestures
   scoped_ptr<internal::SystemGestureEventFilter> system_gesture_filter_;