lowp impl for decal stages

Bug: skia:
Change-Id: If6481d202bf22a95f1dea0c5bf7d84698b63869a
Reviewed-on: https://skia-review.googlesource.com/109241
Commit-Queue: Mike Reed <reed@google.com>
Commit-Queue: Mike Klein <mtklein@chromium.org>
Reviewed-by: Mike Klein <mtklein@chromium.org>
4 files changed