Add new atomic operations and use them in two places.

runtime/vm/atomic_macos.h

 // Copyright (c) 2013, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 #ifndef VM_ATOMIC_MACOS_H_
 #define VM_ATOMIC_MACOS_H_
 
 #if !defined VM_ATOMIC_H_
 #error Do not include atomic_macos.h directly. Use atomic.h instead.
 #endif
 
 #if !defined(TARGET_OS_MACOS)
 #error This file should only be included on Mac OS X builds.
 #endif
 
 namespace dart {
 
+template<typename T> T AtomicOperations::LoadAcquire(T* ptr) {
+  return __atomic_load_n(ptr, __ATOMIC_ACQUIRE);
+}
+
+
+template<typename T> void AtomicOperations::StoreRelease(T* ptr, T val) {
+  __atomic_store_n(ptr, val, __ATOMIC_RELEASE);
+}
+
 
 inline uintptr_t AtomicOperations::FetchAndIncrement(uintptr_t* p) {
   return __sync_fetch_and_add(p, 1);
 }
 
 
 inline void AtomicOperations::IncrementBy(intptr_t* p, intptr_t value) {
   __sync_fetch_and_add(p, value);
 }
 
@@ skipping 24 matching lines @@
 inline uint32_t AtomicOperations::CompareAndSwapUint32(uint32_t* ptr,
                                                        uint32_t old_value,
                                                        uint32_t new_value) {
   return __sync_val_compare_and_swap(ptr, old_value, new_value);
 }
 #endif  // !defined(USING_SIMULATOR_ATOMICS)
 
 }  // namespace dart
 
 #endif  // VM_ATOMIC_MACOS_H_