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 HFSBTreeIterator::SeekToNode(uint32_t node_id) {
  if (node_id >= header_.totalNodes)
    return false;
  size_t offset = node_id * header_.nodeSize;
  if (stream_->Seek(offset, SEEK_SET) != -1) {
    current_leaf_number_ = node_id;
    return true;
  }
  return false;
}

bool HFSBTreeIterator::SeekToNode(uint32_t node_id) {
  if (node_id >= header_.totalNodes)
    return false;
  size_t offset = node_id * header_.nodeSize;
  if (stream_->Seek(offset, SEEK_SET) != -1) {
    current_leaf_number_ = node_id;
    return true;
  }
  return false;
}
