Reland "Remove setting/use of GrPixelConfig in GrBackendTex/RT ctors."

This reverts commit 34aa059c1502d67c9a5f4db449667a8709b69fb9.

Reason for revert: <INSERT REASONING HERE>

Original change's description:
> Revert "Remove setting/use of GrPixelConfig in GrBackendTex/RT ctors."
> 
> This reverts commit ff2181e62e79ffd2ce628fc8c05b5457d4f54163.
> 
> Reason for revert: suspect it's behind Chrome roll failure
> 
> Original change's description:
> > Remove setting/use of GrPixelConfig in GrBackendTex/RT ctors.
> > 
> > Bug: skia:
> > Change-Id: I1466668e3502cd1e6e1f6aed4105e0f626d293dd
> > Reviewed-on: https://skia-review.googlesource.com/138987
> > Commit-Queue: Greg Daniel <egdaniel@google.com>
> > Reviewed-by: Robert Phillips <robertphillips@google.com>
> 
> TBR=egdaniel@google.com,bsalomon@google.com,robertphillips@google.com
> 
> Change-Id: I4cba44858aafffbadc45e18349b93c741d7cfc66
> No-Presubmit: true
> No-Tree-Checks: true
> No-Try: true
> Bug: skia:
> Reviewed-on: https://skia-review.googlesource.com/139220
> Reviewed-by: Ethan Nicholas <ethannicholas@google.com>
> Commit-Queue: Ethan Nicholas <ethannicholas@google.com>

Bug: skia:
Change-Id: Ib1fd10c126862824f3e31c420c697ac749c637f5
Reviewed-on: https://skia-review.googlesource.com/139221
Commit-Queue: Greg Daniel <egdaniel@google.com>
Reviewed-by: Robert Phillips <robertphillips@google.com>
17 files changed