Add presubmit for generated *.gni files.

Add presubmit check to detect a modified BUILD.bazel file which
resulted in a build rule change that requires the GN (*.gni)
files to be updated.

Bug: skia:13485
Change-Id: Ie80af0f2f14af671f104db947c4943ea4b889ab0
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/569118
Reviewed-by: Kevin Lubick <kjlubick@google.com>
Commit-Queue: Chris Mumford <cmumford@google.com>
1 file changed