Notify launcher page with onTransitionChanged event

ui/app_list/views/app_list_main_view.cc

Index: ui/app_list/views/app_list_main_view.cc
diff --git a/ui/app_list/views/app_list_main_view.cc b/ui/app_list/views/app_list_main_view.cc
index 04585c368782a27e6c39869a996ae77b436ec703..73621985d560816aefae210e82548ff520de7f5c 100644
--- a/ui/app_list/views/app_list_main_view.cc
+++ b/ui/app_list/views/app_list_main_view.cc
@@ -125,6 +125,9 @@ void AppListMainView::AddContentsViews() {
   contents_view_->layer()->SetMasksToBounds(true);
 
   delegate_->StartSearch();
+
+  FOR_EACH_OBSERVER(
+      AppListMainViewObserver, observers_, OnContentsViewCreated());
 }
 
 void AppListMainView::ShowAppListWhenReady() {
@@ -167,6 +170,10 @@ void AppListMainView::ModelChanged() {
   pending_icon_loaders_.clear();
   model_ = delegate_->GetModel();
   search_box_view_->ModelChanged();
+
+  FOR_EACH_OBSERVER(
+      AppListMainViewObserver, observers_, OnContentsViewDestroying());
+
   delete contents_view_;
   contents_view_ = NULL;
   if (contents_switcher_view_) {
@@ -261,6 +268,14 @@ void AppListMainView::NotifySearchBoxVisibilityChanged() {
     parent()->SchedulePaint();
 }
 
+void AppListMainView::AddObserver(AppListMainViewObserver* observer) {
+  observers_.AddObserver(observer);
+}
+
+void AppListMainView::RemoveObserver(AppListMainViewObserver* observer) {
+  observers_.RemoveObserver(observer);
+}
+
 void AppListMainView::ActivateApp(AppListItem* item, int event_flags) {
   // TODO(jennyz): Activate the folder via AppListModel notification.
   if (item->GetItemType() == AppListFolderItem::kItemType)