[Media Router] Implement an internal Media Routes observer.

chrome/browser/media/router/media_router_factory.cc

Index: chrome/browser/media/router/media_router_factory.cc
diff --git a/chrome/browser/media/router/media_router_factory.cc b/chrome/browser/media/router/media_router_factory.cc
index 78cbf1844762c3e2463eb545133d93c487c841a3..db43e549737a6f1e142dd9d0c2dfe9034a5c42ff 100644
--- a/chrome/browser/media/router/media_router_factory.cc
+++ b/chrome/browser/media/router/media_router_factory.cc
@@ -69,11 +69,15 @@ content::BrowserContext* MediaRouterFactory::GetBrowserContextToUse(
 
 KeyedService* MediaRouterFactory::BuildServiceInstanceFor(
     BrowserContext* context) const {
+  MediaRouterBase* media_router = nullptr;
 #if defined(OS_ANDROID)
-  return new MediaRouterAndroid(context);
+  media_router = new MediaRouterAndroid(context);
 #else
-  return new MediaRouterMojoImpl(extensions::ProcessManager::Get(context));
+  media_router =
+      new MediaRouterMojoImpl(extensions::ProcessManager::Get(context));
 #endif
+  media_router->Initialize();
+  return media_router;
 }
 
 }  // namespace media_router