[media] Tidy media_service.h member order and comments.

Change-Id: I7263f9f0291b14f5bc0e4831b371465b073ebc96
Reviewed-on: https://chromium-review.googlesource.com/786639Reviewed-by: Xiaohan Wang <xhwang@chromium.org>
Commit-Queue: Dan Sanders <sandersd@chromium.org>
Cr-Commit-Position: refs/heads/master@{#520833}

media/mojo/services/media_service.cc

@@ -38,6 +38,9 @@ void MediaService::OnStart() {
   ref_factory_.reset(new service_manager::ServiceContextRefFactory(
       base::Bind(&service_manager::ServiceContext::RequestQuit,
                  base::Unretained(context()))));
+
+  // TODO(liberato): Remove plumbing for the ref factory once
+  // MediaCodecVideoDecoder no longer takes a ref. (crbug.com/783973)
   mojo_media_client_->Initialize(context()->connector(), ref_factory_.get());
 }
 

media/mojo/services/media_service.h

@@ -62,16 +62,21 @@ class MEDIA_MOJO_EXPORT MediaService : public service_manager::Service,
       mojom::InterfaceFactoryRequest request,
       service_manager::mojom::InterfaceProviderPtr host_interfaces) final;
 
+  MediaLog media_log_;
+  std::unique_ptr<service_manager::ServiceContextRefFactory> ref_factory_;
+
   // Note: Since each instance runs on a different thread, do not share a common
   // MojoMediaClient with other instances to avoid threading issues. Hence using
   // a unique_ptr here.
+  //
+  // Note: Since |*ref_factory_| is passed to |mojo_media_client_|,
+  // |mojo_media_client_| must be destructed before |ref_factory_|.
   std::unique_ptr<MojoMediaClient> mojo_media_client_;
 
+  // Note: Since |&media_log_| is passed to bindings, the bindings must be
+  // destructed first.
   mojo::StrongBindingSet<mojom::InterfaceFactory> interface_factory_bindings_;
 
-  MediaLog media_log_;
-  std::unique_ptr<service_manager::ServiceContextRefFactory> ref_factory_;
-
   service_manager::BinderRegistry registry_;
   mojo::BindingSet<mojom::MediaService> bindings_;
 };