Convert SkRefCnt to std::atomic.

include/private/SkOnce.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 SkOnce_DEFINED
 #define SkOnce_DEFINED
 
@@ skipping 65 matching lines @@
         f(arg);
         // Also known as a store-store/load-store barrier, this makes sure that the writes
         // done before here---in particular, those done by calling f(arg)---are observable
         // before the writes after the line, *done = true.
         //
         // In version control terms this is like saying, "check in the work up
         // to and including f(arg), then check in *done=true as a subsequent change".
         //
         // We'll use this in the fast path to make sure f(arg)'s effects are
         // observable whenever we observe *done == true.
-        sk_release_store(done, true);
+        sk_atomic_store(done, true, sk_memory_order_release);
     }
     lock->release();
 }
 
 // This is our fast path, called all the time.  We do really want it to be inlined.
 template <typename Lock, typename Arg>
 inline void SkOnce(bool* done, Lock* lock, void (*f)(Arg), Arg arg) {
     // When *done == true:
     //   Also known as a load-load/load-store barrier, this acquire barrier makes
     //   sure that anything we read from memory---in particular, memory written by
@@ skipping 33 matching lines @@
 inline void SkOnce(SkOnceFlag* once, void (*func)()) {
     return SkOnce(once, sk_once_no_arg_adaptor, func);
 }
 
 template <typename Lock>
 inline void SkOnce(bool* done, Lock* lock, void (*func)()) {
     return SkOnce(done, lock, sk_once_no_arg_adaptor, func);
 }
 
 #endif  // SkOnce_DEFINED