ash: Update app list button.

ash/shell.cc

Index: ash/shell.cc
diff --git a/ash/shell.cc b/ash/shell.cc
index 9297b0e11837c480898cc96def94d34e96648f40..93cd61f0806611e2c3356b26932925973bce778a 100644
--- a/ash/shell.cc
+++ b/ash/shell.cc
@@ -259,11 +259,11 @@ Shell::~Shell() {
   // TooltipController is deleted with the Shell so removing its references.
   RemovePreTargetHandler(tooltip_controller_.get());
 
-  // AppList needs to be released before shelf layout manager, which is
-  // destroyed with launcher container in the loop below. However, app list
-  // container is now on top of launcher container and released after it.
-  // TODO(xiyuan): Move it back when app list container is no longer needed.
-  app_list_controller_.reset();
+  // AppList needs to clean up it dependency on Shell and closes its opened
+  // UI (if any) before closing all RootWindows. However, the controller
+  // instance is still needed so that sub views (e.g. app menu button on
+  // the shelf) could properly clean up.
+  app_list_controller_->Shutdown();
 
   // Destroy SystemTrayDelegate before destroying the status area(s).
   system_tray_delegate_->Shutdown();
@@ -586,6 +586,10 @@ void Shell::Init() {
   if (!system_tray_delegate_)
     system_tray_delegate_.reset(SystemTrayDelegate::CreateDummyDelegate());
 
+  // Creates app_list_controller_ before the launcher because app list
+  // button observes it for UI visibility.
+  app_list_controller_.reset(new internal::AppListController(this));
+
   // Creates StatusAreaWidget.
   root_window_controller->InitForPrimaryDisplay();
 
@@ -636,21 +640,15 @@ void Shell::ShowContextMenu(const gfx::Point& location_in_screen) {
 }
 
 void Shell::ToggleAppList(aura::Window* window) {
-  // If the context window is not given, show it on the active root window.
-  if (!window)
-    window = GetActiveRootWindow();
-  if (!app_list_controller_)
-    app_list_controller_.reset(new internal::AppListController);
-  app_list_controller_->SetVisible(!app_list_controller_->IsVisible(), window);
+  app_list_controller_->Toggle(window);
 }
 
 bool Shell::GetAppListTargetVisibility() const {
-  return app_list_controller_.get() &&
-      app_list_controller_->GetTargetVisibility();
+  return app_list_controller_->GetTargetVisibility();
 }
 
 aura::Window* Shell::GetAppListWindow() {
-  return app_list_controller_.get() ? app_list_controller_->GetWindow() : NULL;
+  return app_list_controller_->GetWindow();
 }
 
 bool Shell::IsSystemModalWindowOpen() const {