impl SkRuntimeColorFilter::getFlags()

Simply build the skvm program and look to see if in.a.id == out.a.id.

This obviously is conservative, with false negatives possible.  I
haven't done it here, but one possible improvement is to splat uniforms
so constant folding can peer through uniforms too.

Add some basic tests.

Change-Id: I5578ba38ff490b96bf84538025e08d9d352f0320
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/370825
Commit-Queue: Mike Klein <mtklein@google.com>
Reviewed-by: Brian Osman <brianosman@google.com>
2 files changed