  void prepend(absl::string_view data) override {
    FUZZ_ASSERT(start_ >= data.size());
    start_ -= data.size();
    size_ += data.size();
    ::memcpy(mutableStart(), data.data(), data.size());
  }
  void prepend(absl::string_view data) override {
    FUZZ_ASSERT(start_ >= data.size());
    start_ -= data.size();
    size_ += data.size();
    ::memcpy(mutableStart(), data.data(), data.size());
  }