Add query to test our cached convexity

Sometimes our cache of convexity is wrong -- still trying to figure out
what do do about that.

Change-Id: Ie36292b87c4d07fc18643cc91f93be00c577b2ca
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/355616
Reviewed-by: Brian Salomon <bsalomon@google.com>
Commit-Queue: Mike Reed <reed@google.com>
2 files changed