[Media Router] Add a presentation id to MediaRoute mapping in the MR

chrome/browser/media/router/media_router.h

Index: chrome/browser/media/router/media_router.h
diff --git a/chrome/browser/media/router/media_router.h b/chrome/browser/media/router/media_router.h
index 0f8fd4b7386f322a16b2950c04efea0b576f99e2..d951200ad02aa958c2f9f53955dd4fc86529999e 100644
--- a/chrome/browser/media/router/media_router.h
+++ b/chrome/browser/media/router/media_router.h
@@ -189,6 +189,11 @@ class MediaRouter : public KeyedService {
   // there is a change to the media routes, subclass MediaRoutesObserver.
   virtual std::vector<MediaRoute> GetCurrentRoutes() const = 0;
 
+  // Returns the MediaRoute associated with |presentation_id|. Returns nullptr
+  // if no such media route exists.
+  virtual const MediaRoute* GetPresentationRoute(
+      const std::string& presentation_id) const = 0;
+
  private:
   friend class IssuesObserver;
   friend class MediaSinksObserver;