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}
HFSForkReadStream::HFSForkReadStream(HFSIterator* hfs,
                                     const HFSPlusForkData& fork)
    : hfs_(hfs),
      fork_(fork),
      current_extent_(0),
      read_current_extent_(false),
      current_extent_data_(),
      fork_logical_offset_(0) {
}

HFSForkReadStream::HFSForkReadStream(HFSIterator* hfs,
                                     const HFSPlusForkData& fork)
    : hfs_(hfs),
      fork_(fork),
      current_extent_(0),
      read_current_extent_(false),
      current_extent_data_(),
      fork_logical_offset_(0) {
}
