SyncEngine.java

public void writeMutations(List<Mutation> mutations, TaskCompletionSource<Void> userTask) {
  // Write mutations locally using LocalStore
  LocalWriteResult result = localStore.writeLocally(mutations);
  ...
  // Dispatch changes to EventManager who updates active query listeners 
  emitNewSnapsAndNotifyLocalStore(result.getChanges(), /*remoteEvent=*/ null);
  // Tell RemoteStore there're mutations to be sent to the backend
  remoteStore.fillWritePipeline();
}