Adds AppListDelegate to AppList that is notified on visibility changes

ash/app_list/app_list_delegate_impl.cc

Index: ash/app_list/app_list_delegate_impl.cc
diff --git a/ash/app_list/app_list_delegate_impl.cc b/ash/app_list/app_list_delegate_impl.cc
new file mode 100644
index 0000000000000000000000000000000000000000..8f5c63b963670a0f31aecb8796317efd0d46d348
--- /dev/null
+++ b/ash/app_list/app_list_delegate_impl.cc
@@ -0,0 +1,38 @@
+// 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.
+
+#include "ash/app_list/app_list_delegate_impl.h"
+
+#include "ash/common/shelf/app_list_button.h"
+#include "ash/common/shelf/shelf_widget.h"
+#include "ash/common/shelf/wm_shelf.h"
+#include "ash/common/wm_shell.h"
+#include "ash/root_window_controller.h"
+#include "ui/app_list/presenter/app_list.h"
+
+namespace ash {
+
+AppListDelegateImpl::AppListDelegateImpl() {
+  WmShell::Get()->app_list()->set_delegate(this);
+}
+
+AppListDelegateImpl::~AppListDelegateImpl() {
+  WmShell::Get()->app_list()->set_delegate(nullptr);
+}
+
+void AppListDelegateImpl::OnAppListVisibilityChanged(bool visible,
+                                                     int64_t display_id) {
+  WmWindow* root_window = WmShell::Get()->GetRootWindowForDisplayId(display_id);
+  AppListButton* app_list_button =
+      WmShelf::ForWindow(root_window)->shelf_widget()->GetAppListButton();
+  if (!app_list_button)
+    return;
+
+  if (visible)
+    app_list_button->OnAppListShown();
+  else
+    app_list_button->OnAppListDismissed();
+}
+
+}  // namespace ash