Create empty file group to fix Google3 roll.

There was a remaining reference to src/effects/colorfilters:sksl_srcs
at http://google3/third_party/skia/HEAD/BUILD;l=1460;rcl=557792757

Change-Id: Ic8687c07f21b2cc6b73c0c4e6db1cd57eccd48cd
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/745556
Auto-Submit: John Stiles <johnstiles@google.com>
Commit-Queue: John Stiles <johnstiles@google.com>
Reviewed-by: Michael Ludwig <michaelludwig@google.com>
Commit-Queue: Michael Ludwig <michaelludwig@google.com>
3 files changed