Notify launcher page with onTransitionChanged event

ui/app_list/views/app_list_main_view.h

Index: ui/app_list/views/app_list_main_view.h
diff --git a/ui/app_list/views/app_list_main_view.h b/ui/app_list/views/app_list_main_view.h
index a87ae16f213f374064dc64f5e3a245b5d7d25c15..9f08b06bf2e95a7fd383e2d94eb7bddca29425d7 100644
--- a/ui/app_list/views/app_list_main_view.h
+++ b/ui/app_list/views/app_list_main_view.h
@@ -38,7 +38,6 @@ class APP_LIST_EXPORT AppListMainView : public views::View,
                                         public SearchBoxViewDelegate,
                                         public SearchResultListViewDelegate {
  public:
-  // Takes ownership of |delegate|.
   explicit AppListMainView(AppListViewDelegate* delegate);
   ~AppListMainView() override;
 
@@ -72,6 +71,7 @@ class APP_LIST_EXPORT AppListMainView : public views::View,
     return contents_switcher_view_;
   }
   AppListModel* model() { return model_; }
+  AppListViewDelegate* view_delegate() { return delegate_; }
 
   // Returns true if the app list should be centered and in landscape mode.
   bool ShouldCenterWindow() const;