For TextureOp + Alpha texture, xform paint color to dest color space

This is an unfortunate amount of plumbing for this, but benchmarks
confirm that we're better off doing this work in the vertex shader
(with a ubyte attribute) than using a float4 attribute.

Change-Id: I358d330ee452ea0a89cdd725019c8df2686036a0
Reviewed-on: https://skia-review.googlesource.com/144351
Reviewed-by: Brian Salomon <bsalomon@google.com>
Commit-Queue: Brian Osman <brianosman@google.com>
6 files changed