Simple GPU based dithering:

Simple GPU based dithering:

If dithering is turned on, apply an effect that filters the pixel through
the following pipeline:

for each channel c:
  1. Compute quantized colors [low, high] that c is between
  2. Pick high by flipping a coin weighted by (c - low)

R=bsalomon@google.com, egdaniel@google.com, robertphillips@google.com

Author: krajcevski@google.com

Review URL: https://codereview.chromium.org/321253002