cache sksl in runtime colorfilter

With the modified gm, the time (on imac pro) goes from 2.4 to 1.6

Change-Id: I9f940220c129f74771f3b17126657bcf3739044f
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/221176
Commit-Queue: Mike Reed <reed@google.com>
Reviewed-by: Mike Klein <mtklein@google.com>
Reviewed-by: Ethan Nicholas <ethannicholas@google.com>
2 files changed