Add OnDisplayMetricsChanged in DisplayObserver.

ash/shell/window_watcher.cc

 // Copyright (c) 2012 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "ash/shell/window_watcher.h"
 
 #include "ash/display/display_controller.h"
 #include "ash/shelf/shelf.h"
 #include "ash/shelf/shelf_item_delegate_manager.h"
 #include "ash/shelf/shelf_model.h"
@@ skipping 120 matching lines @@
       ShelfModel* model = Shell::GetInstance()->shelf_model();
       int index = model->ItemIndexByID(i->first);
       DCHECK_NE(-1, index);
       model->RemoveItemAt(index);
       id_to_window_.erase(i);
       break;
     }
   }
 }
 
-void WindowWatcher::OnDisplayBoundsChanged(const gfx::Display& display) {
-}
-
 void WindowWatcher::OnDisplayAdded(const gfx::Display& new_display) {
   aura::Window* root = Shell::GetInstance()->display_controller()->
       GetRootWindowForDisplayId(new_display.id());
   workspace_window_watcher_->RootWindowAdded(root);
 }
 
 void WindowWatcher::OnDisplayRemoved(const gfx::Display& old_display) {
   // All windows in the display has already been removed, so no need to
   // remove observers.
 }
 
+void WindowWatcher::OnDisplayMetricsChanged(const gfx::Display&, uint32_t) {
+}
+
 }  // namespace shell
 }  // namespace ash