app_list: Add sync animation.

ui/app_list/app_list_model_observer.h

+// 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.
+
+#ifndef UI_APP_LIST_APP_LIST_MODEL_OBSERVER_H_
+#define UI_APP_LIST_APP_LIST_MODEL_OBSERVER_H_
+
+#include "ui/app_list/app_list_export.h"
+
+namespace app_list {
+
+class APP_LIST_EXPORT AppListModelObserver {
+ public:
+  // Invoked when AppListModel's status has changed.
+  virtual void OnAppListModelStatusChanged() = 0;
+
+ protected:
+  virtual ~AppListModelObserver() {}
+};
+
+}  // namespace app_list
+
+#endif  // UI_APP_LIST_APP_LIST_MODEL_OBSERVER_H_