Revert "Remove texture sampling from GrConfigConversionEffect"

This reverts commit 3bc9bfea5e31b697033e4f0e4c4e4710c34e0387.

Reason for revert: I broke something subtle.

Original change's description:
> Remove texture sampling from GrConfigConversionEffect
> 
> BUG=skia:
> 
> Change-Id: If5df087d3fe11098f468deab5f2fc8beb782cc83
> Reviewed-on: https://skia-review.googlesource.com/10026
> Reviewed-by: Brian Salomon <bsalomon@google.com>
> Commit-Queue: Brian Osman <brianosman@google.com>
> 

TBR=bsalomon@google.com,robertphillips@google.com,brianosman@google.com,reviews@skia.org
NOPRESUBMIT=true
NOTREECHECKS=true
NOTRY=true
BUG=skia:

Change-Id: Icca2f435b30512305f3e483689320a5930dc1467
Reviewed-on: https://skia-review.googlesource.com/10052
Reviewed-by: Brian Osman <brianosman@google.com>
Commit-Queue: Brian Osman <brianosman@google.com>
3 files changed