The hash function will be used by later commits to provide stable ID.

BUG=None
TEST=make && make check

Change-Id: Iea821537214ef56005a06116926d3058172214f1
Reviewed-on: https://chromium-review.googlesource.com/292324


Reviewed-by: Dylan Reid <dgreid@chromium.org>
Commit-Queue: Chinyue Chen <chinyue@chromium.org>
Tested-by: Chinyue Chen <chinyue@chromium.org>