Stop using SkRasterPipeline inside GIF

SkRasterPipeline was overkill, since blending is just comparing to 0.
(Each pixel is either opaque or 0.)

Bug: 760935
Change-Id: I082045010709c07cc2558988ef509816b9d4bc65
Reviewed-on: https://skia-review.googlesource.com/42440
Commit-Queue: Leon Scroggins <scroggo@google.com>
Reviewed-by: Mike Klein <mtklein@chromium.org>
1 file changed