Adds AppListDelegate to AppList that is notified on visibility changes

ui/app_list/presenter/app_list.cc

 // 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.
 
 #include "ui/app_list/presenter/app_list.h"
 
+#include "ui/app_list/presenter/app_list_delegate.h"
+
 namespace app_list {
 
 AppList::AppList() {}
 
 AppList::~AppList() {}
 
 void AppList::BindRequest(mojom::AppListRequest request) {
   bindings_.AddBinding(this, std::move(request));
 }
 
@@ skipping 25 matching lines @@
 }
 
 void AppList::SetAppListPresenter(mojom::AppListPresenterPtr presenter) {
   presenter_ = std::move(presenter);
 }
 
 void AppList::OnTargetVisibilityChanged(bool visible) {
   target_visible_ = visible;
 }
 
-void AppList::OnVisibilityChanged(bool visible) {
+void AppList::OnVisibilityChanged(bool visible, int64_t display_id) {
+  if (visible_ == visible)
+    return;
+
   visible_ = visible;
+  if (delegate_)
+    delegate_->OnAppListVisibilityChanged(visible, display_id);
 }
 
 }  // namespace app_list