Use SkFixedAllocator in SkLinearPipeline and remove the embedding of
the entire pipeline.

Adjust SkFixedAlloc to allow nesting of allocation.

BUG=skia:

GOLD_TRYBOT_URL= https://gold.skia.org/search?issue=4987

Change-Id: Ieeb1b5deaae004b67cee933af9bc19bbfd5a7687
Reviewed-on: https://skia-review.googlesource.com/4987
Commit-Queue: Herb Derby <herb@google.com>
Reviewed-by: Mike Klein <mtklein@chromium.org>
6 files changed