[Media Router] Reland: MediaRouter interfaces with stub implementations.

chrome/browser/media/router/media_sink.cc

Index: chrome/browser/media/router/media_sink.cc
diff --git a/chrome/browser/media/router/media_sink.cc b/chrome/browser/media/router/media_sink.cc
index 87820f6f3aa4bd7189a71f0e2d909ab4203e9ec6..18c3f5192ace826aea25b3686170de6a8e3f5f15 100644
--- a/chrome/browser/media/router/media_sink.cc
+++ b/chrome/browser/media/router/media_sink.cc
@@ -6,8 +6,7 @@
 
 namespace media_router {
 
-MediaSink::MediaSink(const MediaSinkId& sink_id,
-                     const std::string& name)
+MediaSink::MediaSink(const MediaSinkId& sink_id, const std::string& name)
     : sink_id_(sink_id), name_(name) {
 }
 
@@ -18,4 +17,8 @@ bool MediaSink::Equals(const MediaSink& other) const {
   return sink_id_ == other.sink_id_;
 }
 
+bool MediaSink::Empty() const {
+  return sink_id_.empty();
+}
+
 }  // namespace media_router