[Media Router] Design MediaRouter interface with stub implementation.

chrome/browser/media/router/media_route.cc

Index: chrome/browser/media/router/media_route.cc
diff --git a/chrome/browser/media/router/media_route.cc b/chrome/browser/media/router/media_route.cc
index f894761ba80776c0a6262f90ae344ac06c09237b..d6e53ad900fe18158269b5fc303e02781d9d6a59 100644
--- a/chrome/browser/media/router/media_route.cc
+++ b/chrome/browser/media/router/media_route.cc
@@ -22,9 +22,17 @@ MediaRoute::MediaRoute(const MediaRouteId& media_route_id,
       state_(MEDIA_ROUTE_STATE_NEW) {
 }
 
+MediaRoute::MediaRoute()

[mark a. foltz, 2015/03/27 21:21:57]

What is the use case for this?  There's no setters for the fields, so is it just
used as a Null Object?

http://en.wikipedia.org/wiki/Null_Object_pattern

It might be worth adding a brief comment to explain.

[imcheng, 2015/03/30 22:49:08]

Kevin suggested that instead of using a nullptr to represent a situation where a
route is absent (such as the error case of MediaRouteResponse). I added comments
in the header file.

+    : MediaRoute("", MediaSource(), MediaSink(), "", false) {
+}
+
 MediaRoute::~MediaRoute() {
 }
 
+bool MediaRoute::Empty() const {
+  return media_route_id_.empty();
+}
+
 bool MediaRoute::Equals(const MediaRoute& other) const {
   return media_route_id_ == other.media_route_id_;
 }