Add an SkColorSpaceXformer image filter cache

The cache is scoped with the SkColorSpaceXformer object.

This ensures we're not transforming nodes with a degree > 1 multiple
times, and preserves the DAG topology.

Change-Id: I0b072cdac95f9f1c34e0565ed4f258aba986e1ae
Reviewed-on: https://skia-review.googlesource.com/21726
Commit-Queue: Florin Malita <fmalita@chromium.org>
Reviewed-by: Mike Reed <reed@google.com>
5 files changed