make rrect's more self-consistent, check drawable index

Bug: skia:7403
Change-Id: Ifb8f9ffce2acb1c6f1ebc6c733ad3b6c0865409a
Reviewed-on: https://skia-review.googlesource.com/91503
Commit-Queue: Mike Reed <reed@google.com>
Reviewed-by: Kevin Lubick <kjlubick@google.com>
3 files changed