15-bit lowp is dead, long live 8-bit lowp

Change-Id: Icc4b06094aeba3af99b534746f66286d776ef78a
Reviewed-on: https://skia-review.googlesource.com/30920
Reviewed-by: Florin Malita <fmalita@chromium.org>
Commit-Queue: Mike Klein <mtklein@chromium.org>
8 files changed