SkRasterPipeline::compile().

I'm not yet caching these in the blitter, and speed is essentially unchanged in the bench where I am now building and compiling the pipeline only once.  This may not be able to stay a simple std::function after I figure out caching, but for now it's a nice fit.

GOLD_TRYBOT_URL= https://gold.skia.org/search?issue=3911

Change-Id: I9545af589f73baf9f17cb4e6ace9a814c2478fe9
Reviewed-on: https://skia-review.googlesource.com/3911
Reviewed-by: Herb Derby <herb@google.com>
Commit-Queue: Mike Klein <mtklein@chromium.org>
10 files changed