Use a spinlock in SkOnce.

src/ports/SkAtomics_sync.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_sync_DEFINED
 #define SkAtomics_sync_DEFINED
 
@@ skipping 26 matching lines @@
         int32_t before = __sync_val_compare_and_swap(addr, value, value + 1);
 
         if (before == value) {
             return value;
         } else {
             value = before;
         }
     }
 }
 
+static inline __attribute__((always_inline)) bool sk_atomic_cas(int32_t* addr,
+                                                                int32_t before,
+                                                                int32_t after) {
+    return __sync_bool_compare_and_swap(addr, before, after);
+}
+
 static inline __attribute__((always_inline)) void sk_membar_acquire__after_atomic_conditional_inc() { }
 
 #endif