Tidy up memory barriers.

Change-Id: I937ea93e6df1835ecfe2d4bb7d84c24fe7fc097b
diff --git a/runtime/gc/heap-inl.h b/runtime/gc/heap-inl.h
index 9fb5760..af1b26b 100644
--- a/runtime/gc/heap-inl.h
+++ b/runtime/gc/heap-inl.h
@@ -61,7 +61,7 @@
   pre_fence_visitor(obj);
   DCHECK_GT(bytes_allocated, 0u);
   const size_t new_num_bytes_allocated =
-      static_cast<size_t>(num_bytes_allocated_.fetch_add(bytes_allocated)) + bytes_allocated;
+      static_cast<size_t>(num_bytes_allocated_.FetchAndAdd(bytes_allocated)) + bytes_allocated;
   // TODO: Deprecate.
   if (kInstrumented) {
     if (Runtime::Current()->HasStatsEnabled()) {
@@ -200,7 +200,7 @@
     // Only if the allocation succeeded, record the time.
     if (allocated_obj != nullptr) {
       uint64_t allocation_end_time = NanoTime() / kTimeAdjust;
-      heap_->total_allocation_time_.fetch_add(allocation_end_time - allocation_start_time_);
+      heap_->total_allocation_time_.FetchAndAdd(allocation_end_time - allocation_start_time_);
     }
   }
 };