[Media Router] Add Media Router Mojo impl code.

chrome/browser/media/router/media_routes_observer.h

Index: chrome/browser/media/router/media_routes_observer.h
diff --git a/chrome/browser/media/router/media_routes_observer.h b/chrome/browser/media/router/media_routes_observer.h
index b4faa60ab0b6ce2519f0336e4edfc960054cfc92..c9a140fa12c7dd1d42b762ea6f5f3013d2f0a487 100644
--- a/chrome/browser/media/router/media_routes_observer.h
+++ b/chrome/browser/media/router/media_routes_observer.h
@@ -21,9 +21,11 @@ class MediaRoutesObserver {
   explicit MediaRoutesObserver(MediaRouter* router);
   virtual ~MediaRoutesObserver();
 
-  // This function is invoked when the list of routes and their associated
-  // sinks have been updated. Routes included in the list are created either
-  // locally or remotely.
+  // Invoked when the list of routes and their associated sinks have been
+  // updated.
+  // Implementations may not perform operations that modify the Media Router's
+  // observer list. In particular, invoking this observer's destructor within
+  // OnRoutesUpdated will result in undefined behavior.
   virtual void OnRoutesUpdated(const std::vector<MediaRoute>& routes) {}
 
  private: