[Media Router] Remove the extension ID getter from MRMojoImpl

chrome/browser/ui/webui/media_router/media_router_ui.cc

Index: chrome/browser/ui/webui/media_router/media_router_ui.cc
diff --git a/chrome/browser/ui/webui/media_router/media_router_ui.cc b/chrome/browser/ui/webui/media_router/media_router_ui.cc
index 369bcbedaebc6e4802a6d7b394b8dda17f3c9187..679cf901b03c49f3028ad60b563054768654cedb 100644
--- a/chrome/browser/ui/webui/media_router/media_router_ui.cc
+++ b/chrome/browser/ui/webui/media_router/media_router_ui.cc
@@ -18,6 +18,8 @@
 #include "build/build_config.h"
 #include "chrome/browser/browser_process.h"
 #include "chrome/browser/media/router/create_presentation_connection_request.h"
+#include "chrome/browser/media/router/event_page_request_manager.h"
+#include "chrome/browser/media/router/event_page_request_manager_factory.h"
 #include "chrome/browser/media/router/issues_observer.h"
 #include "chrome/browser/media/router/media_router.h"
 #include "chrome/browser/media/router/media_router_factory.h"
@@ -230,9 +232,11 @@ MediaRouterUI::MediaRouterUI(content::WebUI* web_ui)
 
   content::WebContents* wc = web_ui->GetWebContents();
   DCHECK(wc);
+  content::BrowserContext* context = wc->GetBrowserContext();
 
-  router_ =
-      MediaRouterFactory::GetApiForBrowserContext(wc->GetBrowserContext());
+  router_ = MediaRouterFactory::GetApiForBrowserContext(context);
+  event_page_request_manager_ =
+      EventPageRequestManagerFactory::GetApiForBrowserContext(context);
 
   // Allows UI to load extensionview.
   // TODO(haibinlu): limit object-src to current extension once crbug/514866
@@ -858,9 +862,7 @@ const std::set<MediaCastMode>& MediaRouterUI::cast_modes() const {
 }
 
 const std::string& MediaRouterUI::GetRouteProviderExtensionId() const {
-  // TODO(crbug.com/597778): remove reference to MediaRouterMojoImpl
-  return static_cast<MediaRouterMojoImpl*>(router_)
-      ->media_route_provider_extension_id();
+  return event_page_request_manager_->media_route_provider_extension_id();
 }
 
 void MediaRouterUI::SetUIInitializationTimer(const base::Time& start_time) {