Modernize and trim down SkOnce.

src/core/SkGlobalInitialization_core.cpp

 /*
  * Copyright 2016 Google Inc.
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
 #include "SkBitmapProcShader.h"
 #include "SkColorFilter.h"
 #include "SkColorFilterShader.h"
@@ skipping 35 matching lines @@
     // ColorFilter
     SkColorFilter::InitializeFlattenables();
 
     // Xfermode
     SkXfermode::InitializeFlattenables();
 
     // Now initialize any optional/additional effects (implemented in src/ports)
     InitEffects();
 };
 
-SK_DECLARE_STATIC_ONCE(once);
 void SkFlattenable::InitializeFlattenablesIfNeeded() {
-    SkOnce(&once, SkFlattenable::PrivateInitializer::InitCore);
+    static SkOnce once;
+    once(SkFlattenable::PrivateInitializer::InitCore);
 }