Notify launcher page with onTransitionChanged event

ui/app_list/views/contents_view.h

Index: ui/app_list/views/contents_view.h
diff --git a/ui/app_list/views/contents_view.h b/ui/app_list/views/contents_view.h
index ade7fdbf388fe4283e79e5a78e7a565b49903b8e..8290dda0b9cddba46aab72b7d11e042d3a61b94b 100644
--- a/ui/app_list/views/contents_view.h
+++ b/ui/app_list/views/contents_view.h
@@ -78,10 +78,14 @@ class APP_LIST_EXPORT ContentsView : public views::View,
   // True if |state| is the current active laucher page.
   bool IsStateActive(AppListModel::State state) const;
 
-  // Gets the index of a launcher page in |view_model_|, by State. Returns
+  // Gets the index of a launcher page in |view_model_| by State. Returns
   // -1 if there is no view for |state|.
   int GetPageIndexForState(AppListModel::State state) const;
 
+  // Gets the State of a launcher page in |view_model_| by index. Returns
+  // INVALID_STATE if there is no State for |index|.
+  AppListModel::State GetStateForPageIndex(int index) const;
+
   int NumLauncherPages() const;
 
   void Prerender();
@@ -95,7 +99,7 @@ class APP_LIST_EXPORT ContentsView : public views::View,
   void AddBlankPageForTesting();
 
   // Returns the pagination model for the ContentsView.
-  const PaginationModel& pagination_model() { return pagination_model_; }
+  PaginationModel* pagination_model() { return &pagination_model_; }
 
   // Returns search box bounds to use for content views that do not specify
   // their own custom layout.