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..eb5642ddfa62473196283760172a4513a1524bb1 100644
--- a/chrome/browser/media/android/router/media_router_android.h
+++ b/chrome/browser/media/android/router/media_router_android.h
@@ -51,6 +51,7 @@ class MediaRouterAndroid : public MediaRouter {
   void AddIssue(const Issue& issue) override;
   void ClearIssue(const Issue::Id& issue_id) override;
   void OnPresentationSessionDetached(const MediaRoute::Id& route_id) override;
+  bool GetHasLocalRoute() override;

[imcheng, 2015/10/02 17:21:11]

naming: Why not just HasLocalRoute() ? Also, let's mark this method as const for
now.

[apacible, 2015/10/02 18:48:20]

Done.

 
   // The methods called by the Java counterpart.
 
@@ -101,6 +102,10 @@ 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_;