Revert of Convert Color32 code to perfect blend.

Revert of Convert Color32 code to perfect blend. (patchset #6 id:100001 of https://codereview.chromium.org/1098913002/)

Reason for revert:
Xfermode_SrcOver not looking encouraging.  Up to 50% regressions.

https://perf.skia.org/#3242

Original issue's description:
> Convert Color32 code to perfect blend.
> 
> Before we commit to blend_256_round_alt, let's make sure blend_perfect is
> really slower in practice (i.e. regresses on perf.skia.org).
> 
> blend_perfect is really the most desirable algorithm if we can afford it.  Not
> only is it correct, but it's easy to think about and break into correct pieces:
> for instance, its div255() doesn't require any coordination with the multiply.
> 
> This looks like a 30% hit according to microbenches.  That said, microbenches
> said my previous change would be a 20-25% perf improvement, but it didn't end
> up showing a significant effect at a high level.
> 
> As for correctness, I see a bunch of off-by-1 compared to blend_256_round_alt
> (exactly what we'd expect), and one off-by-3 in a GM that looks like it has a
> bunch of overdraw.
> 
> BUG=skia:
> 
> Committed: https://skia.googlesource.com/skia/+/61221e7f87a99765b0e034020e06bb018e2a08c2

TBR=reed@google.com,fmalita@chromium.org,mtklein@chromium.org
NOPRESUBMIT=true
NOTREECHECKS=true
NOTRY=true
BUG=skia:

Committed: https://skia.googlesource.com/skia/+/a4a0aeb74808a0860f3e94588d0ceb0da9fed386

[mtklein, 2015-04-21 15:09:16]

Created Revert of Convert Color32 code to perfect blend.

[commit-bot: I haz the power, 2015-04-21 15:09:25]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1083923006/1

[commit-bot: I haz the power, 2015-04-21 15:09:33]

Committed patchset #1 (id:1) as
https://skia.googlesource.com/skia/+/a4a0aeb74808a0860f3e94588d0ceb0da9fed386