Expand FeatureList to support FieldTrial association.

base/metrics/field_trial.h

 // Copyright (c) 2012 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.
 
 // FieldTrial is a class for handling details of statistical experiments
 // performed by actual users in the field (i.e., in a shipped or beta product).
 // All code is called exclusively on the UI thread currently.
 //
 // The simplest example is an experiment to see whether one of two options
 // produces "better" results across our user population.  In that scenario, UMA
@@ skipping 131 matching lines @@
   // any/all observers that this finalized group number has presumably been used
   // (queried), and will never change. Note that this will force an instance to
   // participate, and make it illegal to attempt to probabilistically add any
   // other groups to the trial.
   int group();
 
   // If the group's name is empty, a string version containing the group number
   // is used as the group name. This causes a winner to be chosen if none was.
   const std::string& group_name();
 
+  // Finalizes the group choice and returns the chosen group, but does not mark
+  // the trial as active - so its state will not be reported until group_name()
+  // or similar is called.
+  const std::string& GetGroupNameWithoutActivation();
+
   // Set the field trial as forced, meaning that it was setup earlier than
   // the hard coded registration of the field trial to override it.
   // This allows the code that was hard coded to register the field trial to
   // still succeed even though the field trial has already been registered.
   // This must be called after appending all the groups, since we will make
   // the group choice here. Note that this is a NOOP for already forced trials.
   // And, as the rest of the FieldTrial code, this is not thread safe and must
   // be done from the UI thread.
   void SetForced();
 
@@ skipping 351 matching lines @@
 
   // List of observers to be notified when a group is selected for a FieldTrial.
   scoped_refptr<ObserverListThreadSafe<Observer> > observer_list_;
 
   DISALLOW_COPY_AND_ASSIGN(FieldTrialList);
 };
 
 }  // namespace base
 
 #endif  // BASE_METRICS_FIELD_TRIAL_H_