In order to optionally report the full hash back to Google, we need to keep it
around in the callback. While a prefix is not the same as a full hash (multiple
full hashes can map to the same prefix), in this case, the callback will only be
called when the full hash matches.
MozReview-Commit-ID: F4WSLZpYrXB
--HG--
extra : rebase_source : da3b16b00729d0aa6ff1765a135b751fcf44c012