[Media Router] Design MediaRouter interface with stub implementation.

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..005765d076ecc0b84982290efb0f7e9b0347d931 100644
--- a/chrome/browser/media/router/media_sink.cc
+++ b/chrome/browser/media/router/media_sink.cc
@@ -8,14 +8,18 @@ namespace media_router {
 
 MediaSink::MediaSink(const MediaSinkId& sink_id,
                      const std::string& name)
-    : sink_id_(sink_id), name_(name) {
-}
+    : sink_id_(sink_id), name_(name) {}
 
-MediaSink::~MediaSink() {
-}
+MediaSink::MediaSink() : MediaSink("", "") {}
+
+MediaSink::~MediaSink() {}
 
 bool MediaSink::Equals(const MediaSink& other) const {
   return sink_id_ == other.sink_id_;
 }
 
+bool MediaSink::Empty() const {
+  return sink_id_.empty();
+}
+
 }  // namespace media_router