Copy logic to preserve CRX files from clobber-state.

BUG=chrome-os-partner:25069
TEST=Manually create an extension cache, factory_reset, ensure that \
  the extension cache remains

Change-Id: I021fb1d616e0d60724187d268410234706125d7c
Reviewed-on: https://chromium-review.googlesource.com/182772
Reviewed-by: Hung-Te Lin <hungte@chromium.org>
Commit-Queue: Jon Salz <jsalz@chromium.org>
Tested-by: Jon Salz <jsalz@chromium.org>
(cherry picked from commit d1715d0b377a0b4dce628ef99080485b98feb489)
Reviewed-on: https://chromium-review.googlesource.com/182765
Reviewed-by: Bowgo Tsai <bowgotsai@chromium.org>
1 file changed