Add a bot to verify that generated SKSL files have not been hand-edited

Bug: skia:6893
Change-Id: I54480ddd1ad1989661393500044f9164a99ce7b0
Reviewed-on: https://skia-review.googlesource.com/27700
Reviewed-by: Ravi Mistry <rmistry@google.com>
Commit-Queue: Eric Boren <borenet@google.com>
9 files changed