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

chrome/browser/media/router/route_request_result.cc

 // Copyright 2016 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "chrome/browser/media/router/route_request_result.h"
 
 #include "base/memory/ptr_util.h"
 #include "chrome/browser/media/router/media_route.h"
 
 namespace media_router {
@@ skipping 16 matching lines @@
 }
 
 RouteRequestResult::RouteRequestResult(std::unique_ptr<MediaRoute> route,
                                        const std::string& presentation_id,
                                        const std::string& error,
                                        ResultCode result_code)
     : route_(std::move(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;
 
 }  // namespace media_router