arc: Use the new InstanceHolder for unittests

components/arc/test/fake_notifications_instance.cc

Index: components/arc/test/fake_notifications_instance.cc
diff --git a/components/arc/test/fake_notifications_instance.cc b/components/arc/test/fake_notifications_instance.cc
index 007ae0b0fe285c34b8cb1bcec1cee42314280c1e..070cb68370874327fc4a8ec5093747f57c24988e 100644
--- a/components/arc/test/fake_notifications_instance.cc
+++ b/components/arc/test/fake_notifications_instance.cc
@@ -6,11 +6,8 @@
 
 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,
@@ -25,8 +22,4 @@ FakeNotificationsInstance::events() const {
   return events_;
 }
 
-void FakeNotificationsInstance::WaitForIncomingMethodCall() {
-  binding_.WaitForIncomingMethodCall();
-}
-
 }  // namespace arc