arc: Use the new InstanceHolder for unittests

ui/arc/notification/arc_notification_manager_unittest.cc

Index: ui/arc/notification/arc_notification_manager_unittest.cc
diff --git a/ui/arc/notification/arc_notification_manager_unittest.cc b/ui/arc/notification/arc_notification_manager_unittest.cc
index f7298c7a4e65ec403df6ef53cc911edfb963866f..866a6b54372de3920d294eb75728b6237c537e12 100644
--- a/ui/arc/notification/arc_notification_manager_unittest.cc
+++ b/ui/arc/notification/arc_notification_manager_unittest.cc
@@ -114,9 +114,7 @@ class ArcNotificationManagerTest : public testing::Test {
   std::unique_ptr<MockMessageCenter> message_center_;
 
   void SetUp() override {
-    mojom::NotificationsInstancePtr arc_notifications_instance;
-    arc_notifications_instance_.reset(
-        new FakeNotificationsInstance(GetProxy(&arc_notifications_instance)));
+    arc_notifications_instance_.reset(new FakeNotificationsInstance());
     service_.reset(new FakeArcBridgeService());
     message_center_.reset(new MockMessageCenter());
 
@@ -125,8 +123,7 @@ class ArcNotificationManagerTest : public testing::Test {
 
     NotificationsObserver observer;
     service_->notifications()->AddObserver(&observer);
-    service_->OnNotificationsInstanceReady(
-        std::move(arc_notifications_instance));
+    service_->notifications()->SetInstance(arc_notifications_instance_.get());
 
     while (!observer.IsReady())
       loop_.RunUntilIdle();
@@ -167,8 +164,6 @@ TEST_F(ArcNotificationManagerTest, NotificationRemovedByChrome) {
     // |notification| gets stale here.
   }
 
-  arc_notifications_instance()->WaitForIncomingMethodCall();
-
   ASSERT_EQ(1u, arc_notifications_instance()->events().size());
   EXPECT_EQ(key, arc_notifications_instance()->events().at(0).first);
   EXPECT_EQ(mojom::ArcNotificationEvent::CLOSED,