arc: Fix regression in handling ARC shelf item.

chrome/browser/ui/ash/launcher/arc_app_window_launcher_controller.cc

Index: chrome/browser/ui/ash/launcher/arc_app_window_launcher_controller.cc
diff --git a/chrome/browser/ui/ash/launcher/arc_app_window_launcher_controller.cc b/chrome/browser/ui/ash/launcher/arc_app_window_launcher_controller.cc
index d6bffcdd19917853d75e8643e8ff8159873f1ab3..9a273987523ca90586e7fc2fbab7c011a1bb41b5 100644
--- a/chrome/browser/ui/ash/launcher/arc_app_window_launcher_controller.cc
+++ b/chrome/browser/ui/ash/launcher/arc_app_window_launcher_controller.cc
@@ -566,6 +566,9 @@ void ArcAppWindowLauncherController::OnTaskOrientationLockRequested(
 
 AppWindowLauncherItemController*
 ArcAppWindowLauncherController::ControllerForWindow(aura::Window* window) {
+  if (!window)
+    return nullptr;
+
   AppWindow* app_window = GetAppWindowForTask(active_task_id_);
   if (app_window &&
       app_window->widget() == views::Widget::GetWidgetForNativeWindow(window)) {
@@ -588,6 +591,8 @@ void ArcAppWindowLauncherController::OnWindowActivated(
     aura::client::ActivationChangeObserver::ActivationReason reason,
     aura::Window* gained_active,
     aura::Window* lost_active) {
+  AppWindowLauncherController::OnWindowActivated(reason, gained_active,
+                                                 lost_active);
   OnTaskSetActive(active_task_id_);
 }