Convert SkRefCnt to std::atomic.

include/private/SkAtomics.h

Index: include/private/SkAtomics.h
diff --git a/include/private/SkAtomics.h b/include/private/SkAtomics.h
index 249723d785865610fb46a00bd3d259e0a22c1d1d..bfe93d8bacd2a9ddf5d59774784f0cd2262f322c 100644
--- a/include/private/SkAtomics.h
+++ b/include/private/SkAtomics.h
@@ -159,32 +159,4 @@ inline int32_t sk_atomic_add(int32_t* ptr, int32_t v) { return sk_atomic_fetch_a
 
 inline int64_t sk_atomic_inc(int64_t* ptr) { return sk_atomic_fetch_add<int64_t>(ptr, +1); }
 
-inline bool sk_atomic_cas(int32_t* ptr, int32_t expected, int32_t desired) {
-    return sk_atomic_compare_exchange(ptr, &expected, desired);
-}
-
-inline void* sk_atomic_cas(void** ptr, void* expected, void* desired) {
-    (void)sk_atomic_compare_exchange(ptr, &expected, desired);
-    return expected;
-}
-
-inline int32_t sk_atomic_conditional_inc(int32_t* ptr) {
-    int32_t prev = sk_atomic_load(ptr);
-    do {
-        if (0 == prev) {
-            break;
-        }
-    } while(!sk_atomic_compare_exchange(ptr, &prev, prev+1));
-    return prev;
-}
-
-template <typename T>
-T sk_acquire_load(T* ptr) { return sk_atomic_load(ptr, sk_memory_order_acquire); }
-
-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