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..509ace4f77df5a6ec62a80d13eb18f19813a482b 100644
--- a/base/metrics/field_trial.h
+++ b/base/metrics/field_trial.h
@@ -251,6 +251,10 @@ class BASE_EXPORT FieldTrial : public RefCounted<FieldTrial> {
   // status.
   void FinalizeGroupChoice();
 
+  // Implements FinalizeGroupChoice() with the added flexibility of being
+  // deadlock-free if |is_locked| is true and the caller is holding a lock.
+  void FinalizeGroupChoiceImpl(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
   // been chosen and has been externally observed via |group()| and the trial
@@ -266,6 +270,10 @@ 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 +525,9 @@ 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);