[Media Router] Design MediaRouter interface with stub implementation.

chrome/browser/media/router/media_route.h

Index: chrome/browser/media/router/media_route.h
diff --git a/chrome/browser/media/router/media_route.h b/chrome/browser/media/router/media_route.h
index a8564f63d0449be3e7080ceed2bf795fcb69b8f7..96b1ebf3e663e4594abdbd69c086dc78c09860a1 100644
--- a/chrome/browser/media/router/media_route.h
+++ b/chrome/browser/media/router/media_route.h
@@ -18,8 +18,7 @@
 namespace media_router {
 
 using RouteRequestId = int64;
-
-class MediaRouteFactory;
+const RouteRequestId kInvalidRouteRequestId = -1;
 
 // For now, a simple transition graph: NEW -> CONNECTED -> CLOSED.
 enum MediaRouteState {
@@ -49,8 +48,14 @@ class MediaRoute {
              const std::string& description,
              bool is_local);
 
+  // Constructs an empty route. Typically we use an empty MediaRoute rather
+  // than nullptr in situations where route is absent.

[xhwang, 2015/04/02 17:13:02]

What's the use case for this? Personally I feel nullptr is more clear and more
efficient.

[imcheng, 2015/04/02 23:05:23]

Reverted back to nullptr. Since a MediaRoute contains a few other objects, it
feels a bit wasteful to contruct an empty instance.

+  MediaRoute();
+
   ~MediaRoute();
 
+  bool Empty() const;
+
   // The media route identifier.
   const MediaRouteId& media_route_id() const { return media_route_id_; }
 
@@ -75,12 +80,12 @@ class MediaRoute {
   bool Equals(const MediaRoute& other) const;
 
  private:
-  const MediaRouteId media_route_id_;
-  const MediaSource media_source_;
-  const MediaSink media_sink_;
-  const std::string description_;
-  const bool is_local_;
-  const MediaRouteState state_;
+  MediaRouteId media_route_id_;
+  MediaSource media_source_;
+  MediaSink media_sink_;
+  std::string description_;
+  bool is_local_;
+  MediaRouteState state_;
 };
 
 }  // namespace media_router