GL: track enabled vertex arrays as a count rather than a mask

Bug: skia:
Change-Id: I46ba29cb32960a415ee1993a7b957ec49c0c56d3
Reviewed-on: https://skia-review.googlesource.com/15520
Commit-Queue: Chris Dalton <csmartdalton@google.com>
Reviewed-by: Brian Salomon <bsalomon@google.com>
3 files changed