converted OverdrawColorFilter to SkSL

Bug: skia:
Change-Id: Idcc0502758df1e60ed131a168b5c9a65a4d834a1
Reviewed-on: https://skia-review.googlesource.com/63840
Commit-Queue: Ethan Nicholas <ethannicholas@google.com>
Reviewed-by: Brian Salomon <bsalomon@google.com>
21 files changed