Add a circle at the cusp to match Adobe Illustrator,
Microsoft Edge, and our own CCPR implementation.
R=reed@google.com,csmartdalton@google.com
Bug: skia:5623
Change-Id: Ia46c910643f373e50c4b30303fcac5f79d77be62
Reviewed-on: https://skia-review.googlesource.com/150370
Commit-Queue: Cary Clark <caryclark@skia.org>
Reviewed-by: Mike Reed <reed@google.com>
