Merge "Offer an ApkSignerEngine implementation." am: 6975f03fd8
am: 2c7da1d5c7

* commit '2c7da1d5c7b5c41736b8f0d63530344ce5f691e7':
  Offer an ApkSignerEngine implementation.

Change-Id: I6e8f9205476ae95bf65f3a6c3d0c0653a8546ffe