Return tuple from GrConvexPolyEffect::Make denoting success or failure.

Change-Id: I1c9cd865c3fd37b5d4c911790713d9ca2283aeee
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/296724
Reviewed-by: Brian Osman <brianosman@google.com>
Commit-Queue: John Stiles <johnstiles@google.com>
6 files changed