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

chrome/browser/media/android/router/media_router_android.h

Index: chrome/browser/media/android/router/media_router_android.h
diff --git a/chrome/browser/media/android/router/media_router_android.h b/chrome/browser/media/android/router/media_router_android.h
index 00f167408ddc132c1af5ea7a7cd0e0c269431278..c362c76bb63fd76d922baed1990f6bca2229a92e 100644
--- a/chrome/browser/media/android/router/media_router_android.h
+++ b/chrome/browser/media/android/router/media_router_android.h
@@ -101,6 +101,10 @@ class MediaRouterAndroid : public MediaRouter {
       PresentationSessionMessagesObserver* observer) override;
   void UnregisterPresentationSessionMessagesObserver(
       PresentationSessionMessagesObserver* observer) override;
+  void RegisterLocalMediaRoutesObserver(
+      LocalMediaRoutesObserver* observer) override;
+  void UnregisterLocalMediaRoutesObserver(
+      LocalMediaRoutesObserver* observer) override;
 
   base::android::ScopedJavaGlobalRef<jobject> java_media_router_;