[Media Router Tests] Add tests for MediaRouterFactory.

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..af65d4b89b1fd604f22f4ed4bf57db7af8be5882 100644
--- a/chrome/browser/media/router/media_router_factory.cc
+++ b/chrome/browser/media/router/media_router_factory.cc
@@ -62,6 +62,11 @@ MediaRouterFactory::MediaRouterFactory()
 MediaRouterFactory::~MediaRouterFactory() {
 }
 
+// static
+MediaRouterFactory* MediaRouterFactory::GetMediaRouterFactory() {
+  return &service_factory.Get();
+}
+
 content::BrowserContext* MediaRouterFactory::GetBrowserContextToUse(
     content::BrowserContext* context) const {
   return chrome::GetBrowserContextRedirectedInIncognito(context);