Adds AppListDelegate to AppList that is notified on visibility changes

ui/app_list/presenter/app_list_presenter_impl.h

Index: ui/app_list/presenter/app_list_presenter_impl.h
diff --git a/ui/app_list/presenter/app_list_presenter_impl.h b/ui/app_list/presenter/app_list_presenter_impl.h
index 616d647bd3e9ef35a52cc9e4b5e2f4704f45b466..4f1ee1bb2183303c61d307642f33e0800787580b 100644
--- a/ui/app_list/presenter/app_list_presenter_impl.h
+++ b/ui/app_list/presenter/app_list_presenter_impl.h
@@ -5,6 +5,8 @@
 #ifndef UI_APP_LIST_PRESENTER_APP_LIST_PRESENTER_IMPL_H_
 #define UI_APP_LIST_PRESENTER_APP_LIST_PRESENTER_IMPL_H_
 
+#include <stdint.h>
+
 #include <memory>
 
 #include "base/compiler_specific.h"
@@ -84,6 +86,10 @@ class APP_LIST_PRESENTER_EXPORT AppListPresenterImpl
   // Starts show/hide animation.
   void ScheduleAnimation();
 
+  // Returns the id of the display containing the app list, if visible. If not
+  // visible returns kInvalidDisplayId.
+  int64_t GetDisplayId();
+
   // aura::client::FocusChangeObserver overrides:
   void OnWindowFocused(aura::Window* gained_focus,
                        aura::Window* lost_focus) override;