Atomics overhaul.

include/ports/SkAtomics_std.h

+#ifndef SkAtomics_std_DEFINED
+#define SkAtomics_std_DEFINED
+
+// We try not to depend on the C++ standard library,
+// but these uses of <atomic> should all inline, so we don't feel to bad here.
+#include <atomic>
+
+template <typename T>
+T sk_atomic_load(const T* ptr, sk_memory_order mo) {
+    const std::atomic<T>* ap = reinterpret_cast<const std::atomic<T>*>(ptr);
+    return std::atomic_load_explicit(ap, (std::memory_order)mo);
+}
+
+template <typename T>
+void sk_atomic_store(T* ptr, T val, sk_memory_order mo) {
+    std::atomic<T>* ap = reinterpret_cast<std::atomic<T>*>(ptr);
+    return std::atomic_store_explicit(ap, val, (std::memory_order)mo);
+}
+
+template <typename T>
+T sk_atomic_fetch_add(T* ptr, T val, sk_memory_order mo) {
+    std::atomic<T>* ap = reinterpret_cast<std::atomic<T>*>(ptr);
+    return std::atomic_fetch_add_explicit(ap, val, (std::memory_order)mo);
+}
+
+template <typename T>
+bool sk_atomic_compare_exchange(T* ptr, T* expected, T desired,
+                                sk_memory_order success,
+                                sk_memory_order failure) {
+    std::atomic<T>* ap = reinterpret_cast<std::atomic<T>*>(ptr);
+    return std::atomic_compare_exchange_strong_explicit(ap, expected, desired,
+                                                        (std::memory_order)success,
+                                                        (std::memory_order)failure);
+}
+
+#endif//SkAtomics_std_DEFINED