Move the outer mesh into a member of GrAATriangulator

Bug: skia:10419
Change-Id: I547e7c63b9d7ad9abeb6377f4a31d6d671bb5030
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/350482
Commit-Queue: Chris Dalton <csmartdalton@google.com>
Reviewed-by: Jim Van Verth <jvanverth@google.com>
2 files changed