add GM for exercising interesting paths in SkVMBlitter

It's not drawing anything earthshattering, but it does act as an easy
way to exercise some interesting code paths in SkVMBlitter, here first
program caching based on shader program and not shader identity.

With today's shader caching patches, this makes 2 calls to
skvm::Builder::done(), JITing the program, while if you patched this in
at head you'd see 3.  I'd like it to get down to 1 by converting paint
colors to color shaders.

Change-Id: I042f4d44a792b46e5543794c853e4ef0d95b11ec
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/252029
Commit-Queue: Mike Klein <mtklein@google.com>
Reviewed-by: Mike Reed <reed@google.com>
2 files changed