Fix deadlock issue with AllStatesToString

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 9a7e5d26f25cf7bd3069b7fd2fe4dd65bdf65f1c..2a3b97f602fca4b0b9ffa39999ead8c88be8ffa7 100644
--- a/base/metrics/field_trial.h
+++ b/base/metrics/field_trial.h
@@ -249,7 +249,7 @@ class BASE_EXPORT FieldTrial : public RefCounted<FieldTrial> {
   // Ensures that a group is chosen, if it hasn't yet been. The field trial
   // might yet be disabled, so this call will *not* notify observers of the
   // status.
-  void FinalizeGroupChoice();
+  void FinalizeGroupChoice(bool is_locked);
 
   // Returns the trial name and selected group name for this field trial via
   // the output parameter |active_group|, but only if the group has already
@@ -266,6 +266,10 @@ class BASE_EXPORT FieldTrial : public RefCounted<FieldTrial> {
   // untouched.
   bool GetState(State* field_trial_state);
 
+  // Does the same thing as above, but is deadlock-free if the caller is holding
+  // a lock.
+  bool GetStateWhileLocked(State* field_trial_state);
+
   // Returns the group_name. A winner need not have been chosen.
   std::string group_name_internal() const { return group_name_; }
 
@@ -517,9 +521,9 @@ class BASE_EXPORT FieldTrialList {
   // Remove an observer.
   static void RemoveObserver(Observer* observer);
 
-  // Grabs the lock and adds the field trial to the allocator. This should only
-  // be called from FinalizeGroupChoice().
-  static void OnGroupFinalized(FieldTrial* field_trial);
+  // Grabs the lock if necessary and adds the field trial to the allocator. This
+  // should only be called from FinalizeGroupChoice().
+  static void OnGroupFinalized(bool is_locked, FieldTrial* field_trial);
 
   // Notify all observers that a group has been finalized for |field_trial|.
   static void NotifyFieldTrialGroupSelection(FieldTrial* field_trial);