Add the SandboxedDMGParser and wire it up to the DownloadProtectionService.

BUG=496898,464083
R=isherman@chromium.org, kenrb@chromium.org, mattm@chromium.org, thestig@chromium.org

Review URL: https://codereview.chromium.org/1299223006 .

Cr-Commit-Position: refs/heads/master@{#344876}
bool HFSIterator::SeekToBlock(uint64_t block) {
  uint64_t offset = block * volume_header_.blockSize;
  off_t rv = stream_->Seek(offset, SEEK_SET);
  return rv >= 0 && static_cast<uint64_t>(rv) == offset;
}

bool HFSIterator::SeekToBlock(uint64_t block) {
  uint64_t offset = block * volume_header_.blockSize;
  off_t rv = stream_->Seek(offset, SEEK_SET);
  return rv >= 0 && static_cast<uint64_t>(rv) == offset;
}
