chroot hook: Unmerge old libchrome when switching to new slot

libchrome is being uprevved to r369476

BUG=b/26772882
TEST=./build_packages
CQ-DEPEND=CL:323378

Change-Id: Id677c3b9f2d8288eb1be0a3fdf617225626e374c
Reviewed-on: https://chromium-review.googlesource.com/323435
Commit-Ready: Alex Vakulenko <avakulenko@google.com>
Tested-by: Alex Vakulenko <avakulenko@google.com>
Reviewed-by: Mike Frysinger <vapier@chromium.org>
1 file changed