Hold allocator lock while fetching 'used' count.

base/debug/activity_tracker_unittest.cc

Index: base/debug/activity_tracker_unittest.cc
diff --git a/base/debug/activity_tracker_unittest.cc b/base/debug/activity_tracker_unittest.cc
index 26c0b5136cfe61d838eae23119246a6a6ad1bb45..4132848885b549eac32144f30a07182f57604834 100644
--- a/base/debug/activity_tracker_unittest.cc
+++ b/base/debug/activity_tracker_unittest.cc
@@ -74,6 +74,7 @@ class ActivityTrackerTest : public testing::Test {
     GlobalActivityTracker* global_tracker = GlobalActivityTracker::Get();
     if (!global_tracker)
       return 0;
+    base::AutoLock autolock(global_tracker->thread_tracker_allocator_lock_);
     return global_tracker->thread_tracker_allocator_.cache_used();
   }