Adds AppListDelegate to AppList that is notified on visibility changes

ui/app_list/presenter/app_list_delegate.h

+// Copyright 2017 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.
+
+#ifndef UI_APP_LIST_PRESENTER_APP_LIST_DELEGATE_H_
+#define UI_APP_LIST_PRESENTER_APP_LIST_DELEGATE_H_
+
+#include <stdint.h>
+
+#include "ui/app_list/presenter/app_list_presenter_export.h"
+
+namespace app_list {
+
+class APP_LIST_PRESENTER_EXPORT AppListDelegate {
+ public:
+  // Called when the visility of the app list changes. |display_id| is the
+  // id of the display containing the app list.
+  virtual void OnAppListVisibilityChanged(bool visible, int64_t display_id) = 0;
+
+ protected:
+  virtual ~AppListDelegate() {}
+};
+
+}  // namespace app_list
+
+#endif  // UI_APP_LIST_PRESENTER_APP_LIST_DELEGATE_H_