message: Provide a default implementation for Cord based WritableFile::Append operation.
diff: @@ -780,7 +780,10 @@ class WritableFile {
  #if defined(TF_CORD_SUPPORT)
  // \brief Append 'data' to the file.
  virtual tensorflow::Status Append(const absl::Cord& cord) {
  - return errors::Unimplemented("Append(absl::Cord) is not implemented");
  + for (StringPiece chunk : cord.Chunks()) {
  + TF_RETURN_IF_ERROR(Append(chunk));
  + }
  + return tensorflow::Status::OK();
  }
  #endif
  