* Output to floating point framebuffers so that results are not truncated
   to 8 bit normalized values.
 * Tighten the epsilon from 1/255 to 0.0005. May need further tweaking as
   more GPUs are tested.
 * Explicitly check for -inf and inf values when they were previously
   rounded to 0 and 255.
 * Explicitly check for clamping of overflowed normalized floats by
   providing the expectations instead of computing them.

BUG=angleproject:1044

Change-Id: I8410cf61fe79a9919fb0db7e415bf97b2d0abd9e
Reviewed-on: https://chromium-review.googlesource.com/281191Reviewed-by: Olli Etuaho <oetuaho@nvidia.com>
Tested-by: Geoff Lang <geofflang@chromium.org>
Reviewed-by: Jamie Madill <jmadill@chromium.org>