Eliminate some clutter in SkFlattenable

Eliminate some clutter in SkFlattenable

The Registrar class is unnecessary, as SkFlattenable factory
registration is now handled via initialization routines that can just
call the Register function directly.

Also, no need to lazily initialize gCount to 0, as initializing an int
to a constant value does not require dynamic initialization.  (C++
actually guarantees zero initialization of global ints anyway, but
existing practice in Skia appears to favor the explicit "= 0").

Relatedly, this requires removing the unused/unimplemented
SkLayerDrawLooper::MyRegistrar class.  And removing that allows Clang
to realize that SkLayerDrawLooper::fTopRec is unneeded too, so remove
that too to squelch the compiler warning/error.

This doesn't change any public API.
TBR=reed@google.com

Committed: https://skia.googlesource.com/skia/+/00d6e515e5835f7df6163ceb5f5ceb1770552bf7

[mdempsky, 2015-09-24 02:06:54]

The CQ bit was checked by mdempsky@chromium.org to run a CQ dry run

[commit-bot: I haz the power, 2015-09-24 02:07:19]

Dry run: CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1361323002/1
View timeline at
 https://chromium-cq-status.appspot.com/patch-timeline/1361323002/1

[commit-bot: I haz the power, 2015-09-24 02:07:21]

Note for Reviewers:
The CQ is waiting for an approval.
If you believe that the CL is not ready yet, or if you would like to L-G-T-M
with comments then please uncheck the CQ checkbox.

Waiting for LGTM from valid reviewer(s) till 2015-09-24 08:07 UTC

[commit-bot: I haz the power, 2015-09-24 02:08:25]

The CQ bit was unchecked by commit-bot@chromium.org

[commit-bot: I haz the power, 2015-09-24 02:08:26]

Dry run: Try jobs failed on following builders:
  Build-Ubuntu-Clang-x86_64-Debug-Trybot on client.skia.compile (JOB_FAILED,
http://build.chromium.org/p/client.skia.compile/builders/Build-Ubuntu-Clang-x...)

[mdempsky, 2015-09-24 03:53:34]

The CQ bit was checked by mdempsky@chromium.org to run a CQ dry run

[commit-bot: I haz the power, 2015-09-24 03:53:48]

Dry run: CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1361323002/20001
View timeline at
 https://chromium-cq-status.appspot.com/patch-timeline/1361323002/20001

[mdempsky, 2015-09-24 04:16:49]

mdempsky@chromium.org changed reviewers:
+ mtklein@google.com

[mdempsky, 2015-09-24 04:21:30]

mtklein: PTAL.

Technically, SkFlattenable::Registrar was a public class, but it feels to me
like it's just an implementation detail of how the
SK_DEFINE_FLATTENABLE_REGISTRAR_ENTRY macro.  Feel free to edit the CL
description and/or remove the TBR if you think otherwise.

[commit-bot: I haz the power, 2015-09-24 08:07:00]

The CQ bit was unchecked by commit-bot@chromium.org

[commit-bot: I haz the power, 2015-09-24 08:07:00]

Dry run: No LGTM from a valid reviewer yet. Please ask for an LGTM from a
full Skia committer

[mtklein, 2015-09-24 22:03:57]

The CQ bit was checked by mtklein@google.com

[mtklein, 2015-09-24 22:03:57]

lgtm

Very LGTM.

Please do continue to TBR=reed on things like this exactly as you've done here. 
There's a blanket implicit LGTM to anything removing code from Skia's public
API.  We just want to make sure Someone With Good Judgement LGTMs changes that
_add_ to it.

[commit-bot: I haz the power, 2015-09-24 22:04:10]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1361323002/20001
View timeline at
 https://chromium-cq-status.appspot.com/patch-timeline/1361323002/20001

[commit-bot: I haz the power, 2015-09-24 22:04:49]

Committed patchset #2 (id:20001) as
https://skia.googlesource.com/skia/+/00d6e515e5835f7df6163ceb5f5ceb1770552bf7