only create new instance if needed for colorspacexformer

just an experiment to address performance when imagefilters are cached.

Bug: skia:
Change-Id: Ic1033c897d0a569b46a339fb3ae7f8f961882953
Reviewed-on: https://skia-review.googlesource.com/21395
Commit-Queue: Mike Reed <reed@google.com>
Reviewed-by: Florin Malita <fmalita@chromium.org>
25 files changed