SkConvertPixels: Add Alpha8 fast path

BUG:692936

Change-Id: I8394554764b1f46bd8eaabb0194d52f361d477c1
Reviewed-on: https://skia-review.googlesource.com/8826
Commit-Queue: Matt Sarett <msarett@google.com>
Reviewed-by: Mike Klein <mtklein@chromium.org>
1 file changed