Fix problem where field trials using kExpirationYearInFuture could get disabled.

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 265 matching lines @@
 // Class with a list of all active field trials.  A trial is active if it has
 // been registered, which includes evaluating its state based on its probaility.
 // Only one instance of this class exists.
 class BASE_EXPORT FieldTrialList {
  public:
   // Define a separator character to use when creating a persistent form of an
   // instance.  This is intended for use as a command line argument, passed to a
   // second process to mimic our state (i.e., provide the same group name).
   static const char kPersistentStringSeparator;  // Currently a slash.
 
-  // Define expiration year in future. It is initialized to two years from Now.
-  static int kExpirationYearInFuture;
+  // Year that is guaranteed to not be expired when instantiating a field trial
+  // via |FactoryGetFieldTrial()|. Set to two years from the build date.

[Ilya Sherman, 2013/01/08 21:18:53]

nit: Please use two spaces after the period for consistency with the surrounding
code.

[Alexei Svitkine (slow), 2013/01/09 15:24:58]

Done.

+  static int kExpirationYearNotExpired;

[Ilya Sherman, 2013/01/08 21:18:53]

nit: I think the previous name was slightly clearer for casual users of the API

[Alexei Svitkine (slow), 2013/01/08 21:56:22]

The reason I changed the name is because after this change, the date may not
necessarily be in the future. (e.g. if it's an old build and the build date is
over two years old, then this date may be in the past). So I chose a name that
communicates exactly what it's guaranteeing (i.e. the trial won't be expired),
rather than talking about "future", which is practically not relevant to users.

Let me know if you still want me to change it (and if so to what), or if this is
okay given my explanation.

[Ilya Sherman, 2013/01/08 22:02:04]

I agree that the new name is more technically correct, but I think that most
clients would rather have the name be clearer in its intent, even if it might be
strictly false.  IMO kExpirationYearNotExpired is a little hard to parse.  Some
other potential names: kNoExpirationYear, kNeverExpireYear, kUnexpiredYear,
kExpirationYearNeverExpire (though this last one has a similar issue w.r.t.
being kind of hard to parse).  WDYT?

[Alexei Svitkine (slow), 2013/01/09 15:24:58]

Changed to kNoExpirationYear.

 
   // Observer is notified when a FieldTrial's group is selected.
   class BASE_EXPORT Observer {
    public:
     // Notify observers when FieldTrials's group is selected.
     virtual void OnFieldTrialGroupFinalized(const std::string& trial_name,
                                             const std::string& group_name) = 0;
 
    protected:
     virtual ~Observer();
@@ skipping 137 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_