Refactor to put SkXfermode_opts inside SK_OPTS_NS.

src/core/Sk4px.h

Index: src/core/Sk4px.h
diff --git a/src/core/Sk4px.h b/src/core/Sk4px.h
index ffde1af504f682504034839b5db142eecf76fa39..1c8ed0df713c3636a2f692e8f859e8f6a60212da 100644
--- a/src/core/Sk4px.h
+++ b/src/core/Sk4px.h
@@ -12,13 +12,6 @@
 #include "SkColor.h"
 #include "SkColorPriv.h"
 
-// This file may be included multiple times by .cpp files with different flags, leading
-// to different definitions.  Usually that doesn't matter because it's all inlined, but
-// in Debug modes the compilers may not inline everything.  So wrap everything in an
-// anonymous namespace to give each includer their own silo of this code (or the linker
-// will probably pick one randomly for us, which is rarely correct).
-namespace {
-
 // 1, 2 or 4 SkPMColors, generally vectorized.
 class Sk4px : public Sk16b {
 public:
@@ -226,8 +219,6 @@ private:
     typedef Sk16b INHERITED;
 };
 
-}  // namespace
-
 #ifdef SKNX_NO_SIMD
     #include "../opts/Sk4px_none.h"
 #else