TSAN startup fix

base/metrics/field_trial_param_associator.cc

 // Copyright 2016 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "base/metrics/field_trial_param_associator.h"
 
 #include "base/metrics/field_trial.h"
 
 namespace base {
 
 FieldTrialParamAssociator::FieldTrialParamAssociator() {}
 FieldTrialParamAssociator::~FieldTrialParamAssociator() {}
 
 // static
 FieldTrialParamAssociator* FieldTrialParamAssociator::GetInstance() {
   return Singleton<FieldTrialParamAssociator,
                    LeakySingletonTraits<FieldTrialParamAssociator>>::get();
 }
 
 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;
 
   field_trial_params_[key] = params;
   return true;
 }
 
 bool FieldTrialParamAssociator::GetFieldTrialParams(
     const std::string& trial_name,
     FieldTrialParams* params) {
   AutoLock scoped_lock(lock_);
 
   const std::string group_name = FieldTrialList::FindFullName(trial_name);
   const FieldTrialKey key(trial_name, group_name);
   if (!ContainsKey(field_trial_params_, key))
     return false;
 
   *params = field_trial_params_[key];
   return true;
 }
 
 void FieldTrialParamAssociator::ClearAllParamsForTesting() {
   AutoLock scoped_lock(lock_);
   field_trial_params_.clear();
 }
 
 }  // namespace base