Use a spinlock in SkOnce.

src/ports/SkAtomics_win.h

 /*
  * Copyright 2013 Google Inc.
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
 #ifndef SkAtomics_win_DEFINED
 #define SkAtomics_win_DEFINED
 
@@ skipping 35 matching lines @@
         long before = _InterlockedCompareExchange(reinterpret_cast<long*>(addr), value + 1, value);
 
         if (before == value) {
             return value;
         } else {
             value = before;
         }
     }
 }
 
+static inline bool sk_atomic_cas(int32_t* addr, int32_t before, int32_t after) {
+    return _InterlockedCompareExchange(reinterpret_cast<long*>(addr), after, before) == before;
+}
+
 static inline void sk_membar_acquire__after_atomic_conditional_inc() { }
 
 #endif