MediaRouterAction: Only observe Media Routes when there is a local route.

chrome/browser/media/router/mock_media_router.h

Index: chrome/browser/media/router/mock_media_router.h
diff --git a/chrome/browser/media/router/mock_media_router.h b/chrome/browser/media/router/mock_media_router.h
index 14aeb44cdd5c2758815e1623255271e2e7953def..eae2e1d12f590926e5887d4267d4aea557e41b9f 100644
--- a/chrome/browser/media/router/mock_media_router.h
+++ b/chrome/browser/media/router/mock_media_router.h
@@ -67,6 +67,10 @@ class MockMediaRouter : public MediaRouter {
                void(PresentationSessionMessagesObserver* observer));
   MOCK_METHOD1(UnregisterPresentationSessionMessagesObserver,
                void(PresentationSessionMessagesObserver* observer));
+  MOCK_METHOD1(RegisterLocalMediaRoutesObserver,
+               void(LocalMediaRoutesObserver* observer));
+  MOCK_METHOD1(UnregisterLocalMediaRoutesObserver,
+               void(LocalMediaRoutesObserver* observer));
 };
 
 }  // namespace media_router