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

chrome/browser/media/router/route_request_result.cc

Index: chrome/browser/media/router/route_request_result.cc
diff --git a/chrome/browser/media/router/route_request_result.cc b/chrome/browser/media/router/route_request_result.cc
index 4c50e409f48d2dbbfce982369a625826dbc9bd68..a65b7d71fdd4d5aa357c73abf48c8c0f37dd1108 100644
--- a/chrome/browser/media/router/route_request_result.cc
+++ b/chrome/browser/media/router/route_request_result.cc
@@ -34,8 +34,10 @@ RouteRequestResult::RouteRequestResult(std::unique_ptr<MediaRoute> route,
       presentation_id_(presentation_id),
       error_(error),
       result_code_(result_code) {
-  if (route_)
+  if (route_) {
     presentation_url_ = route_->media_source().url();
+    route_->set_presentation_id(presentation_id);

[imcheng, 2017/03/10 23:53:45]

Two comments:

1) It isn't clear to me how this MediaRoute with presentation ID will end up in
MediaRouterBase / InternalMediaRoutesObserver -- it seems they need to be
informed when a route is created.
2) The extension itself does not pass back presentation IDs in MediaRoutes. We
need to ensure that the presentation ID is preserved when OnRoutesUpdated
happens.

+  }
 }
 
 RouteRequestResult::~RouteRequestResult() = default;