Add SkRasterPipeline::dump().

Entirely for debugging.

TBR=herb@google.com

GOLD_TRYBOT_URL= https://gold.skia.org/search?issue=4871

Change-Id: I6d6972c40b11854441f566c12516a2ec8c75c78f
Reviewed-on: https://skia-review.googlesource.com/4871
Reviewed-by: Herb Derby <herb@google.com>
Reviewed-by: Mike Klein <mtklein@chromium.org>
Commit-Queue: Mike Klein <mtklein@chromium.org>
2 files changed