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 <[email protected]> Commit-Queue: Jon Salz <[email protected]> Tested-by: Jon Salz <[email protected]> (cherry picked from commit d1715d0b377a0b4dce628ef99080485b98feb489) Reviewed-on: https://chromium-review.googlesource.com/182765 Reviewed-by: Bowgo Tsai <[email protected]>