Reland "Add a GpuGM class for GPU-only tests"

This is a reland of f5efa7890272bd7a3daf052af5ffa546903eb9a6

Original change's description:
> Add a GpuGM class for GPU-only tests
>
> Bug: skia:8731
> Change-Id: Ic81f21621c0183bb356601eb663fa1ee334bca55
> Reviewed-on: https://skia-review.googlesource.com/c/189134
> Reviewed-by: Brian Osman <brianosman@google.com>
> Reviewed-by: Mike Klein <mtklein@google.com>
> Commit-Queue: Chris Dalton <csmartdalton@google.com>

TBR=mtklein@google.com

Bug: skia:8731
Change-Id: Ia322d7e9280b67ebea1edbefc820cae72cd9c3a6
Reviewed-on: https://skia-review.googlesource.com/c/190148
Reviewed-by: Chris Dalton <csmartdalton@google.com>
Commit-Queue: Chris Dalton <csmartdalton@google.com>
23 files changed