[webnfc] Add default implementation for nfc mojo service.

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 1cc0c86a1e2884e3eb1599028822c30e680aeb49..91733068a18e197e96b287cf273f81e957f33930 100644
--- a/content/browser/frame_host/render_frame_host_impl.cc
+++ b/content/browser/frame_host/render_frame_host_impl.cc
@@ -78,6 +78,7 @@
 #include "content/public/common/isolated_world_ids.h"
 #include "content/public/common/url_constants.h"
 #include "content/public/common/url_utils.h"
+#include "device/nfc/nfc_impl.h"
 #include "ui/accessibility/ax_tree.h"
 #include "ui/accessibility/ax_tree_update.h"
 #include "ui/gfx/geometry/quad_f.h"
@@ -1936,6 +1937,8 @@ void RenderFrameHostImpl::RegisterMojoServices() {
                    base::Unretained(this)));
   }
 
+  GetServiceRegistry()->AddService(base::Bind(&device::NFCImpl::Create));

[ncarter (slow), 2016/04/26 22:28:26]

Do we plan to implement a c++, non-stub version of NFC on some platform?

If so, then this is fine.

If not, I'd prefer that it be clearer here that the purpose of this line is to
installs a stub implementation (either via comment, or by explicitly
instantiating a stub-looking object like NfcImplDefault()).

[Reilly Grant (use Gerrit), 2016/04/26 22:35:33]

Actually, now that I think about it again I'd rather we not have a stub
implementation at all. If an implementation is not available the Mojo service
binding should simply fail (return from the service factory callback without
binding the interface request).

+
   if (!frame_mojo_shell_)
     frame_mojo_shell_.reset(new FrameMojoShell(this));