Port SkRefCnt.h to new SkAtomics.h

include/core/SkAtomics.h

 #ifndef SkAtomics_DEFINED
 #define SkAtomics_DEFINED
 
 // This file is not part of the public Skia API.
 #include "SkTypes.h"
 
 enum sk_memory_order {
     sk_memory_order_relaxed,
     sk_memory_order_consume,
     sk_memory_order_acquire,
@@ skipping 16 matching lines @@
                                 sk_memory_order success = sk_memory_order_seq_cst,
                                 sk_memory_order failure = sk_memory_order_seq_cst);
 #if defined(_MSC_VER)
     #include "../ports/SkAtomics_std.h"
 #elif !defined(SK_BUILD_FOR_IOS) && defined(__ATOMIC_RELAXED)
     #include "../ports/SkAtomics_atomic.h"
 #else
     #include "../ports/SkAtomics_sync.h"
 #endif
 
+inline void sk_memory_barrier(sk_memory_order mo) {
+    int junk;
+    (void)sk_atomic_fetch_add(&junk, 42, mo);
+}
+
 // From here down we have shims for our old atomics API, to be weaned off of.
 // We use the default sequentially-consistent memory order to make things simple
 // and to match the practical reality of our old _sync and _win implementations.
 
 inline int32_t sk_atomic_inc(int32_t* ptr)            { return sk_atomic_fetch_add(ptr, +1); }
 inline int32_t sk_atomic_dec(int32_t* ptr)            { return sk_atomic_fetch_add(ptr, -1); }
 inline int32_t sk_atomic_add(int32_t* ptr, int32_t v) { return sk_atomic_fetch_add(ptr,  v); }
 
 inline int64_t sk_atomic_inc(int64_t* ptr) { return sk_atomic_fetch_add<int64_t>(ptr, +1); }
 
@@ skipping 26 matching lines @@
     return sk_atomic_load(ptr, sk_memory_order_relaxed);
 }
 
 template <typename T>
 void sk_release_store(T* ptr, T val) { sk_atomic_store(ptr, val, sk_memory_order_release); }
 
 inline void sk_membar_acquire__after_atomic_dec() {}
 inline void sk_membar_acquire__after_atomic_conditional_inc() {}
 
 #endif//SkAtomics_DEFINED