Add new atomic operations and use them in two places.

runtime/vm/atomic_win.h

Index: runtime/vm/atomic_win.h
diff --git a/runtime/vm/atomic_win.h b/runtime/vm/atomic_win.h
index 38ec10a1f8996841078d0dec585ed38f8fe84601..b761559f70b58a71c9840d63242022a34d8877eb 100644
--- a/runtime/vm/atomic_win.h
+++ b/runtime/vm/atomic_win.h
@@ -13,8 +13,20 @@
 #error This file should only be included on Windows builds.
 #endif
 
+#include <atomic>
+
 namespace dart {
 
+template<typename T> T AtomicOperations::LoadAcquire(T* ptr) {
+  return atomic_load_explicit(ptr, memory_order_acquire);
+}
+
+
+template<typename T> void AtomicOperations::StoreRelease(T* ptr, T val) {
+  return atomic_store_explicit(ptr, val, memory_order_release);
+}
+
+
 inline uintptr_t AtomicOperations::FetchAndIncrement(uintptr_t* p) {
 #if defined(HOST_ARCH_X64)
   return static_cast<uintptr_t>(