Method as_string

src/butil/strings/string_piece.h:262–265

  }

  STRING_TYPE as_string() const {
    // std::string doesn't like to take a NULL pointer even with a 0 size.
    return empty() ? STRING_TYPE() : STRING_TYPE(data(), size());
  }

  // Return the first/last character, UNDEFINED when StringPiece is empty.
  char front() const { return *ptr_; }