Add a blend-wrong mode to SkRasterPipelineBlitter.

This keeps correct linear blending as the only option exericsed,
but it should be easy to see how to turn on blend-wrong mode.

Change-Id: I7d87ef8ed00e8990107bd36b826f8d229d930400
Reviewed-on: https://skia-review.googlesource.com/8125
Reviewed-by: Brian Osman <brianosman@google.com>
Reviewed-by: Matt Sarett <msarett@google.com>
Commit-Queue: Mike Klein <mtklein@chromium.org>
3 files changed