docker - Record the skia git hash.

Puts the git hash in an easy place for dependent docker files to retrieve it from.

Bug: skia:
Change-Id: I096c25554df76779b088d6aab91ddce31304ffde
Reviewed-on: https://skia-review.googlesource.com/136067
Reviewed-by: Kevin Lubick <kjlubick@google.com>
Commit-Queue: Joe Gregorio <jcgregorio@google.com>
1 file changed