TSAN startup fix

base/metrics/field_trial_param_associator.cc

Index: base/metrics/field_trial_param_associator.cc
diff --git a/base/metrics/field_trial_param_associator.cc b/base/metrics/field_trial_param_associator.cc
index 0230b8a8a8d39082d166052eb00303e4ff03919e..4a4e361b5d51318fde718940ee07413874d18974 100644
--- a/base/metrics/field_trial_param_associator.cc
+++ b/base/metrics/field_trial_param_associator.cc
@@ -21,11 +21,10 @@ bool FieldTrialParamAssociator::AssociateFieldTrialParams(
     const std::string& trial_name,
     const std::string& group_name,
     const FieldTrialParams& params) {
-  AutoLock scoped_lock(lock_);
-
   if (FieldTrialList::IsTrialActive(trial_name))
     return false;
 
+  AutoLock scoped_lock(lock_);
   const FieldTrialKey key(trial_name, group_name);
   if (ContainsKey(field_trial_params_, key))
     return false;