Reland "Add support for unpremul image sources in the GPU backend"

This reverts commit cbf64e3634ee7adfddf221e7ba525672ee226580.

Reason for revert: Ancestral CLs have re-landed.

Original change's description:
> Revert "Add support for unpremul image sources in the GPU backend"
> 
> This reverts commit f06240de2c4583c8d8ef2e798dd4636e6cfe8f47.
> 
> Reason for revert: I think this requires the skcms codec change to re-land,
> 
> Original change's description:
> > Add support for unpremul image sources in the GPU backend
> > 
> > Change-Id: Ib940fa0d658fff0b2dd923abfcc5ca4a49b2b38b
> > Reviewed-on: https://skia-review.googlesource.com/148397
> > Commit-Queue: Brian Osman <brianosman@google.com>
> > Reviewed-by: Mike Klein <mtklein@google.com>
> 
> TBR=mtklein@google.com,bsalomon@google.com,brianosman@google.com
> 
> Change-Id: Ib9358cf858c3c0887322503a4b021e08a0ac4cd5
> No-Presubmit: true
> No-Tree-Checks: true
> No-Try: true
> Reviewed-on: https://skia-review.googlesource.com/148861
> Reviewed-by: Brian Osman <brianosman@google.com>
> Commit-Queue: Brian Osman <brianosman@google.com>

TBR=mtklein@google.com,bsalomon@google.com,brianosman@google.com

# Not skipping CQ checks because original CL landed > 1 day ago.

Change-Id: I20d8d17f5cc6ed1a359c0f7af1c96bf5304f6885
Reviewed-on: https://skia-review.googlesource.com/149804
Reviewed-by: Brian Osman <brianosman@google.com>
Commit-Queue: Brian Osman <brianosman@google.com>
16 files changed