[m59] dither when converting to 4444 NOTREECHECKS=true NOTRY=true NOPRESUBMIT=true Bug: 720105 Change-Id: I2a3b8a56795403077151ccebed978a94f2350def Change-Id: I2a3b8a56795403077151ccebed978a94f2350def Reviewed-on: https://skia-review.googlesource.com/18021 Reviewed-by: Mike Klein <mtklein@chromium.org> Commit-Queue: Mike Klein <mtklein@chromium.org>