Adds AppListDelegate to AppList that is notified on visibility changes

ui/app_list/presenter/app_list_presenter.mojom

 // Copyright 2016 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.
 
 module app_list.mojom;
 
 import "services/ui/public/interfaces/window_manager_constants.mojom";
 
 // TODO(msw): Rename this file to app_list.mojom; move to ash?
 // TODO(msw): Ash should implement the app list and presenter; chrome should
 //            just push data about its apps into the app list interface.
 
 // Implemented by ash. Used by chrome to set the presenter interface.
 interface AppList {
   // Set the app list presenter interface, to let ash trigger Chrome's app list.
   SetAppListPresenter(AppListPresenter presenter);
 
   // Notify the app list that the presenter's [target] visibility changed.
   OnTargetVisibilityChanged(bool visible);
-  OnVisibilityChanged(bool visible);
+
+  // |display_id| gives the display containing the app list.
+  OnVisibilityChanged(bool visible, int64 display_id);
 };
 
 // Implemented by chrome. Used by ash to actually show and dismiss the app list.
 interface AppListPresenter {
   // Show the app list on the specified display.
   Show(int64 display_id);
 
   // Dismiss the app list.
   Dismiss();
 
   // Show the app list (on the specified display) if it is hidden; hide the
   // app list if it is shown.
   ToggleAppList(int64 display_id);
 };