Retry "SkRasterPipelineBlitter: support A8"...

    ...preferring SkA8_Coverage_Blitter over SkRasterPipelineBlitter.

I think we could make this work with SkRasterPipelineBlitter (tell it, draw white in Src mode with this mask), but the existing blitter is pretty hard to beat in efficiency and correctness.

CQ_INCLUDE_TRYBOTS=skia.primary:Perf-Ubuntu-Clang-GCE-CPU-AVX2-x86_64-Debug-MSAN,Test-Ubuntu-GCC-GCE-CPU-AVX2-x86_64-Release-SKNX_NO_SIMD


Change-Id: I72df9995c63f3334d8111c59711818cb5ed1e63c
Reviewed-on: https://skia-review.googlesource.com/6627
Reviewed-by: Mike Klein <mtklein@chromium.org>
Commit-Queue: Mike Klein <mtklein@chromium.org>
6 files changed