Notify launcher page with onTransitionChanged event

ui/app_list/app_list_model.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_H_
 #define UI_APP_LIST_APP_LIST_MODEL_H_
 
 #include <string>
 #include <vector>
 
@@ skipping 25 matching lines @@
  public:
   enum Status {
     STATUS_NORMAL,
     STATUS_SYNCING,  // Syncing apps or installing synced apps.
   };
 
   enum State {
     STATE_APPS,
     STATE_SEARCH_RESULTS,
     STATE_START,
+    STATE_CUSTOM_LAUNCHER_PAGE,
 
     INVALID_STATE,
   };
 
   typedef ui::ListModel<SearchResult> SearchResults;
 
   AppListModel();
   ~AppListModel() override;
 
   void AddObserver(AppListModelObserver* observer);
@@ skipping 127 matching lines @@
   State state_;
   ObserverList<AppListModelObserver, true> observers_;
   bool folders_enabled_;
 
   DISALLOW_COPY_AND_ASSIGN(AppListModel);
 };
 
 }  // namespace app_list
 
 #endif  // UI_APP_LIST_APP_LIST_MODEL_H_