NoBarrier_Load()/NoBarrier_Store() for manipulating activated field.

base/metrics/field_trial.h

Index: base/metrics/field_trial.h
diff --git a/base/metrics/field_trial.h b/base/metrics/field_trial.h
index 8a84baea34e338ec3d449cda5c4010f11595ea01..f7626aa048c9c1b33edbb206a507674b8489c150 100644
--- a/base/metrics/field_trial.h
+++ b/base/metrics/field_trial.h
@@ -63,6 +63,7 @@
 #include <string>
 #include <vector>
 
+#include "base/atomicops.h"
 #include "base/base_export.h"
 #include "base/command_line.h"
 #include "base/feature_list.h"
@@ -143,8 +144,9 @@ class BASE_EXPORT FieldTrial : public RefCounted<FieldTrial> {
     static constexpr size_t kExpectedInstanceSize = 8;
 
     // Whether or not this field trial is activated. This is really just a
-    // boolean but marked as a uint32_t for portability reasons.
-    uint32_t activated;
+    // boolean but using a 32 bit value for portability reasons. It should be
+    // accessed via NoBarrier_Load()/NoBarrier_Store().
+    subtle::Atomic32 activated;
 
     // Size of the pickled structure, NOT the total size of this entry.
     uint32_t pickle_size;