[Media Router] Remove the extension ID getter from MRMojoImpl

chrome/browser/media/router/mojo/media_router_mojo_impl.cc

 // Copyright 2015 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/mojo/media_router_mojo_impl.h"
 
 #include <stddef.h>
 
 #include <utility>
 
@@ skipping 203 matching lines @@
     for (auto& observer : routes_query->observers)
       observer.OnRoutesUpdated(routes, joinable_route_ids);
   } else {
     DVLOG_WITH_INSTANCE(1)
         << "Received routes update without any active observers: "
         << media_source;
   }
   RemoveInvalidRouteControllers(routes);
 }
 
-const std::string& MediaRouterMojoImpl::media_route_provider_extension_id()
-    const {
-  return event_page_request_manager_->media_route_provider_extension_id();
-}
-
 void MediaRouterMojoImpl::RouteResponseReceived(
     const std::string& presentation_id,
     bool is_incognito,
     std::vector<MediaRouteResponseCallback> callbacks,
     bool is_join,
     const base::Optional<MediaRoute>& media_route,
     const base::Optional<std::string>& error_text,
     RouteRequestResult::ResultCode result_code) {
   std::unique_ptr<RouteRequestResult> result;
   if (!media_route) {
@@ skipping 776 matching lines @@
 
 void MediaRouterMojoImpl::OnMediaControllerCreated(
     const MediaRoute::Id& route_id,
     bool success) {
   DVLOG_WITH_INSTANCE(1) << "OnMediaControllerCreated: " << route_id
                          << (success ? " was successful." : " failed.");
   MediaRouterMojoMetrics::RecordMediaRouteControllerCreationResult(success);
 }
 
 }  // namespace media_router