Refactor to put SkXfermode_opts inside SK_OPTS_NS.

Refactor to put SkXfermode_opts inside SK_OPTS_NS.

Without this refactor I was getting warnings previously about having code
inside namespace SK_OPTS_NS (e.g. namespace sse2, namespace neon) referring to
code inside an anonymous namespace (Sk4px, SkPMFloat, Sk4f, etc) [1].

That low-level code was in an anonymous namespace to allow multiple independent
copies of its methods to be instantiated without the linker getting confused /
offended about violating the One Definition Rule.  This was only happening in
Debug mode where the methods were not being inlined.

To fix this all, I've force-inlined the methods of the low-level code and
removed the anonymous namespace.

BUG=skia:4117
[1] Here is what those errors looked like:

In file included from ../../../../src/core/SkOpts.cpp:18:0:
../../../../src/opts/SkXfermode_opts.h:193:7: error: 'portable::Sk4pxXfermode' has a field 'portable::Sk4pxXfermode::fProc4' whose type uses the anonymous namespace [-Werror]
 class Sk4pxXfermode : public SkProcCoeffXfermode {
       ^
../../../../src/opts/SkXfermode_opts.h:193:7: error: 'portable::Sk4pxXfermode' has a field 'portable::Sk4pxXfermode::fAAProc4' whose type uses the anonymous namespace [-Werror]
../../../../src/opts/SkXfermode_opts.h:235:7: error: 'portable::SkPMFloatXfermode' has a field 'portable::SkPMFloatXfermode::fProcF' whose type uses the anonymous namespace [-Werror]
 class SkPMFloatXfermode : public SkProcCoeffXfermode {
       ^
cc1plus: all warnings being treated as errors

Committed: https://skia.googlesource.com/skia/+/b07bee3121680b53b98b780ac08d14d374dd4c6f

[mtklein_C, 2015-08-12 16:05:42]

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

[commit-bot: I haz the power, 2015-08-12 16:05:51]

Dry run: CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1286093004/1
View timeline at
 https://chromium-cq-status.appspot.com/patch-timeline/1286093004/1

[mtklein_C, 2015-08-12 16:10:39]

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

[commit-bot: I haz the power, 2015-08-12 16:13:52]

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

[commit-bot: I haz the power, 2015-08-12 16:13:52]

Dry run: This issue passed the CQ dry run.

[djsollen, 2015-08-12 17:21:23]

lgtm

[mtklein, 2015-08-12 17:22:44]

The CQ bit was checked by mtklein@google.com

[commit-bot: I haz the power, 2015-08-12 17:22:59]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1286093004/1
View timeline at
 https://chromium-cq-status.appspot.com/patch-timeline/1286093004/1

[commit-bot: I haz the power, 2015-08-12 17:23:41]

Committed patchset #1 (id:1) as
https://skia.googlesource.com/skia/+/b07bee3121680b53b98b780ac08d14d374dd4c6f

[mtklein, 2015-08-12 18:56:25]

A revert of this CL (patchset #1 id:1) has been created in
https://codereview.chromium.org/1284333002/ by mtklein@google.com.

The reason for reverting is: Maybe causing test / gold problems?.