Fix typo in tranferring from regular add to Atomic increment.

runtime/vm/pages.cc

 // Copyright (c) 2012, 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.
 
 #include "vm/pages.h"
 
 #include "platform/assert.h"
 #include "vm/compiler_stats.h"
 #include "vm/gc_marker.h"
 #include "vm/gc_sweeper.h"
@@ skipping 825 matching lines @@
   // Make code pages writable.
   WriteProtectCode(false);
 
   // Save old value before GCMarker visits the weak persistent handles.
   SpaceUsage usage_before = GetCurrentUsage();
 
   // Mark all reachable old-gen objects.
   bool collect_code = FLAG_collect_code && ShouldCollectCode();
   GCMarker marker(heap_);
   marker.MarkObjects(isolate, this, invoke_api_callbacks, collect_code);
-  AtomicOperations::FetchAndIncrementBy(&(usage_.used_in_words),
-                                        marker.marked_words());
+  usage_.used_in_words = marker.marked_words();
 
   int64_t mid1 = OS::GetCurrentTimeMicros();
 
   // Abandon the remainder of the bump allocation block.
   AbandonBumpAllocation();
   // Reset the freelists and setup sweeping.
   freelist_[HeapPage::kData].Reset();
   freelist_[HeapPage::kExecutable].Reset();
 
   int64_t mid2 = OS::GetCurrentTimeMicros();
@@ skipping 364 matching lines @@
     return 0;
   } else {
     ASSERT(total_time >= gc_time);
     int result = static_cast<int>((static_cast<double>(gc_time) /
                                    static_cast<double>(total_time)) * 100);
     return result;
   }
 }
 
 }  // namespace dart