arc: Use the new InstanceHolder for unittests

components/arc/test/fake_notifications_instance.cc

 // Copyright 2016 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 "components/arc/test/fake_notifications_instance.h"
 
 namespace arc {
 
-FakeNotificationsInstance::FakeNotificationsInstance(
-    mojo::InterfaceRequest<mojom::NotificationsInstance> request)
-    : binding_(this, std::move(request)) {}
-
-FakeNotificationsInstance::~FakeNotificationsInstance() {}
+FakeNotificationsInstance::FakeNotificationsInstance() = default;
+FakeNotificationsInstance::~FakeNotificationsInstance() = default;
 
 void FakeNotificationsInstance::SendNotificationEventToAndroid(
     const mojo::String& key,
     mojom::ArcNotificationEvent event) {
   events_.emplace_back(key, event);
 }
 
 void FakeNotificationsInstance::Init(mojom::NotificationsHostPtr host_ptr) {}
 
 const std::vector<std::pair<mojo::String, mojom::ArcNotificationEvent>>&
 FakeNotificationsInstance::events() const {
   return events_;
 }
 
-void FakeNotificationsInstance::WaitForIncomingMethodCall() {
-  binding_.WaitForIncomingMethodCall();
-}
-
 }  // namespace arc