Add empty filegroups to appease G3

No-Try: true
Change-Id: I2e8eee566fa95ec46e4358f076f0122ef541d05b
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/765521
Auto-Submit: Kevin Lubick <kjlubick@google.com>
Reviewed-by: John Stiles <johnstiles@google.com>
Commit-Queue: John Stiles <johnstiles@google.com>
3 files changed