minor refactor to SkRasterPipeline::BuildPipeline

I don't see any reason to have it be static...

Change-Id: I0fdc9c0629e2194c469f7c9c696d1bb55ffbc98a
Reviewed-on: https://skia-review.googlesource.com/18455
Reviewed-by: Mike Klein <mtklein@chromium.org>
Commit-Queue: Mike Klein <mtklein@chromium.org>
2 files changed