Revert "Revert "clamp to premul when reading premul sRGB""

This reverts commit 2e018f548d76b0688f9873c683cffc681fec40ec.

Reason for revert: doesn't appear to have been the roll problem.

Original change's description:
> Revert "clamp to premul when reading premul sRGB"
> 
> This reverts commit 04e10da8362a0dcabd795a4ad53f617719ca0d20.
> 
> Reason for revert: roll?
> 
> Change-Id: Id0a8dcd62763bd6eddde120c513ca97e098a4268
> Reviewed-on: https://skia-review.googlesource.com/6022
> Commit-Queue: Mike Klein <mtklein@chromium.org>
> Reviewed-by: Mike Klein <mtklein@chromium.org>
> 

TBR=mtklein@chromium.org,reviews@skia.org,brianosman@google.com
NOPRESUBMIT=true
NOTREECHECKS=true
NOTRY=true

Change-Id: I399ca5e728ce6766c6707682c4c6b685681ffdeb
Reviewed-on: https://skia-review.googlesource.com/6025
Commit-Queue: Mike Klein <mtklein@chromium.org>
Reviewed-by: Mike Klein <mtklein@chromium.org>
7 files changed