Notify launcher page with onTransitionChanged event

ui/app_list/views/app_list_main_view.h

 // Copyright 2013 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_VIEWS_APP_LIST_MAIN_VIEW_H_
 #define UI_APP_LIST_VIEWS_APP_LIST_MAIN_VIEW_H_
 
 #include <string>
 
 #include "base/memory/scoped_vector.h"
 #include "base/memory/weak_ptr.h"
+#include "base/observer_list.h"
 #include "base/timer/timer.h"
 #include "ui/app_list/app_list_export.h"
 #include "ui/app_list/views/apps_grid_view_delegate.h"
 #include "ui/app_list/views/search_box_view_delegate.h"
 #include "ui/app_list/views/search_result_list_view_delegate.h"
 #include "ui/views/view.h"
 
 namespace views {
 class Widget;
 }
 
 namespace app_list {
 
 class AppListItem;
 class AppListModel;
 class AppListViewDelegate;
 class ApplicationDragAndDropHost;
 class ContentsSwitcherView;
 class ContentsView;
 class PaginationModel;
 class SearchBoxView;
 
+class AppListMainViewObserver {
+ public:
+  // Invoked after a new contents view is created.
+  virtual void OnContentsViewCreated() {}
+
+  // Invoked before the contens view is destroyed.
+  virtual void OnContentsViewDestroying() {}
+
+ protected:
+  virtual ~AppListMainViewObserver() {}
+};
+
 // AppListMainView contains the normal view of the app list, which is shown
 // when the user is signed in.
 class APP_LIST_EXPORT AppListMainView : public views::View,
                                         public AppsGridViewDelegate,
                                         public SearchBoxViewDelegate,
                                         public SearchResultListViewDelegate {
  public:
   // Takes ownership of |delegate|.
   explicit AppListMainView(AppListViewDelegate* delegate);
   ~AppListMainView() override;
@@ skipping 28 matching lines @@
     return contents_switcher_view_;
   }
   AppListModel* model() { return model_; }
 
   // Returns true if the app list should be centered and in landscape mode.
   bool ShouldCenterWindow() const;
 
   // Called when the search box's visibility is changed.
   void NotifySearchBoxVisibilityChanged();
 
+  void AddObserver(AppListMainViewObserver* observer);
+  void RemoveObserver(AppListMainViewObserver* observer);
+
  private:
   class IconLoader;
 
   // Adds the ContentsView and the ContentsSwitcherView.
   void AddContentsViews();
 
   // Gets the PaginationModel owned by the AppsGridView.
   PaginationModel* GetAppsPaginationModel();
 
   // Loads icon image for the apps in the selected page of |pagination_model_|.
@@ skipping 31 matching lines @@
   ContentsSwitcherView* contents_switcher_view_;
 
   // A timer that fires when maximum allowed time to wait for icon loading has
   // passed.
   base::OneShotTimer<AppListMainView> icon_loading_wait_timer_;
 
   ScopedVector<IconLoader> pending_icon_loaders_;
 
   base::WeakPtrFactory<AppListMainView> weak_ptr_factory_;
 
+  ObserverList<AppListMainViewObserver, true> observers_;
+
   DISALLOW_COPY_AND_ASSIGN(AppListMainView);
 };
 
 }  // namespace app_list
 
 #endif  // UI_APP_LIST_VIEWS_APP_LIST_MAIN_VIEW_H_