Function NewWritableFile

src/leveldb/include/leveldb/env.h:332–334

    return target_->NewRandomAccessFile(f, r);
  }
  Status NewWritableFile(const std::string& f, WritableFile** r) override {
    return target_->NewWritableFile(f, r);
  }
  Status NewAppendableFile(const std::string& f, WritableFile** r) override {
    return target_->NewAppendableFile(f, r);
  }