Batch across matrix changes in drawVertices and add GM to test.

Change-Id: I6b08d37781e3c715a1d9d8c9729667ec78625836
Reviewed-on: https://skia-review.googlesource.com/7949
Commit-Queue: Brian Salomon <bsalomon@google.com>
Reviewed-by: Robert Phillips <robertphillips@google.com>
4 files changed