test.cc

void InMemoryURLIndex::Init(...) {
  BrowserThread::PostTaskAndReplyWithResult(
      BrowserThread::DB, FROM_HERE,
      base::Bind(&URLIndexPrivateData::Init,
                 base::Unretained(private_data_.get()),
                 sequence_token_),
      base::Bind(&InMemoryURLIndex::OnPrivateDataInitDone,
                 AsWeakPtr(),
                 base::Passed(&private_data_)));
}

void InMemoryURLIndex::OnPrivateDataInitDone(
    scoped_ptr<URLIndexPrivateData> private_data,
    bool result) {
  private_data_ = private_data.Pass();
}