Add annotation.

Author: mrober

transport/transport-runtime/src/main/java/com/google/android/datatransport/runtime/scheduling/jobscheduling/Uploader.java

@@ -17,6 +17,7 @@
 import android.content.Context;
 import android.net.ConnectivityManager;
 import android.net.NetworkInfo;
+import androidx.annotation.RestrictTo;
 import androidx.annotation.VisibleForTesting;
 import com.google.android.datatransport.Encoding;
 import com.google.android.datatransport.runtime.EncodedPayload;
@@ -111,6 +112,7 @@ public void upload(TransportContext transportContext, int attemptNumber, Runnabl
         });
   }
 
+  @RestrictTo(RestrictTo.Scope.LIBRARY_GROUP)
   public BackendResponse logAndUpdateState(TransportContext transportContext, int attemptNumber) {
     TransportBackend backend = backendRegistry.get(transportContext.getBackendName());
     long maxNextRequestWaitMillis = 0;