externs needed for cpu/gpu switch

Bug: skia:
Change-Id: I39de7abdc54872ae983bbb8a7e88a8b9d93a952b
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/206919
Reviewed-by: Kevin Lubick <kjlubick@google.com>
Commit-Queue: Nathaniel Nifong <nifong@google.com>
1 file changed