Move media::mojom::RemoterFactory to content, add ContentBrowserClient API.

content/browser/frame_host/render_frame_host_impl.cc

Index: content/browser/frame_host/render_frame_host_impl.cc
diff --git a/content/browser/frame_host/render_frame_host_impl.cc b/content/browser/frame_host/render_frame_host_impl.cc
index 524168e7fd86d30d90b82f00d8608e04decf3b12..857cd1ef343c66ce041788a68a1b9db8a82777ec 100644
--- a/content/browser/frame_host/render_frame_host_impl.cc
+++ b/content/browser/frame_host/render_frame_host_impl.cc
@@ -96,7 +96,9 @@
 #include "device/vibration/vibration_manager_impl.h"
 #include "device/wake_lock/wake_lock_service_context.h"
 #include "media/base/media_switches.h"
+#include "media/media_features.h"
 #include "media/mojo/interfaces/media_service.mojom.h"
+#include "media/mojo/interfaces/remoting.mojom.h"
 #include "mojo/public/cpp/bindings/associated_interface_ptr.h"
 #include "mojo/public/cpp/bindings/strong_binding.h"
 #include "services/service_manager/public/cpp/connector.h"
@@ -2249,6 +2251,23 @@ void RenderFrameHostImpl::RegisterMojoInterfaces() {
   }
 #endif
 
+#if BUILDFLAG(ENABLE_MEDIA_REMOTING)
+  // Add a no-op RemoterFactory binder. Embedders that support media remoting
+  // will override this via their ContentBrowserClient.
+  class NullRemoterFactory final : public media::mojom::RemoterFactory {

[Ben Goodger (Google), 2016/11/16 18:56:13]

Since the renderer requires this always, rather than replacing having the
embedder replace the factory (which seems a little scary, if the call out to
RenderRenderFrameMojoInterfaces ever moves around), why not just add a
special-purpose method to the browser client to bind this request & have the
canonical RemoteFactory factory live here?

[miu, 2016/11/16 22:30:06]

Done. Prior to this, I had assumed it was normal/SOP for the service-side
binding to be optional--based on whether support was present in the
embedder--and so it would be fine if some embedders did not register with the
InterfaceRegistry. AFAIK, this was never made clear in any Mojo-in-Chromium
documentation.

+   public:
+    void Create(media::mojom::RemotingSourcePtr source,
+                media::mojom::RemoterRequest remoter) final {}
+    static void CreateRemoterFactory(
+        media::mojom::RemoterFactoryRequest request) {
+      mojo::MakeStrongBinding(base::MakeUnique<NullRemoterFactory>(),
+                              std::move(request));
+    }
+  };
+  GetInterfaceRegistry()->AddInterface(
+      base::Bind(&NullRemoterFactory::CreateRemoterFactory));
+#endif  // BUILDFLAG(ENABLE_MEDIA_REMOTING)
+
   GetContentClient()->browser()->RegisterRenderFrameMojoInterfaces(
       GetInterfaceRegistry(), this);
 }