drawVertices in GPU backend uses drawVustomMesh implementation.

This still allows batching across view matrix changes but does not batch
across SkVertices that have different attributes.

Bug: skia:12720
Change-Id: I34b58e2ae3aa7330b1fe3280b9448197e2bb68b0
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/491047
Reviewed-by: Greg Daniel <egdaniel@google.com>
Commit-Queue: Brian Salomon <bsalomon@google.com>
8 files changed