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() {}

HFSForkReadStream::~HFSForkReadStream() {}
