Feature to disable field trials in old versions of Chromium. Field trials...

base/metrics/field_trial.h

Index: base/metrics/field_trial.h
===================================================================
--- base/metrics/field_trial.h	(revision 71223)
+++ base/metrics/field_trial.h	(working copy)
@@ -66,6 +66,7 @@
 #include <map>
 #include <string>
 
+#include "base/gtest_prod_util.h"
 #include "base/lock.h"
 #include "base/ref_counted.h"
 #include "base/time.h"
@@ -77,22 +78,24 @@
   typedef int Probability;  // Probability type for being selected in a trial.
 
   // A return value to indicate that a given instance has not yet had a group
-  // assignment (and hence is not yet participating in the trial).
-  static const int kNotParticipating;
+  // assignment (and hence group assignment is not yet finalized in the trial).
+  static const int kNotFinalized;
 
-  // Provide an easy way to assign all remaining probability to a group.  Note
-  // that this will force an instance to participate, and make it illegal to
-  // attempt to probabalistically add any other groups to the trial.  When doing
-  // A/B tests with timings, it is often best to define all groups, so that
-  // histograms will get unique names via the MakeName() methods.
-  static const Probability kAllRemainingProbability;
+  // Every field trial is reserved a kDefaultGroupNumber. If a group assigement
+  // is not done, when group() is called, all the remaining probability is
+  // assigned to a group and its number is kDefaultGroupNumber.
+  // When doing A/B tests with timings, it is often best to define all groups,
+  // so that histograms will get unique names via the MakeName() methods.
+  static const int kDefaultGroupNumber;
 
   // The name is used to register the instance with the FieldTrialList class,
   // and can be used to find the trial (only one trial can be present for each
   // name).
   // Group probabilities that are later supplied must sum to less than or equal
   // to the total_probability.
-  FieldTrial(const std::string& name, Probability total_probability);
+  FieldTrial(const std::string& name, Probability total_probability,
+             const std::string& default_group_name, const int year,
+             const int month, const int day_of_month);
 
   // Establish the name and probability of the next group in this trial.
   // Sometimes, based on construction randomization, this call may causes the
@@ -103,9 +106,10 @@
   std::string name() const { return name_; }
 
   // Return the randomly selected group number that was assigned.
-  // Return kNotParticipating if the instance is not participating in the
-  // experiment.
-  int group() const { return group_; }
+  // Return kDefaultGroupNumber if the instance is in the default group. This
+  // call finalizes the FieldTrial and group assignment is completed when this
+  // method is called.
+  int group();
 
   // If the field trial is not in an experiment, this returns the empty string.
   // if the group's name is empty, a name of "_" concatenated with the group
@@ -121,10 +125,36 @@
   static void EnableBenchmarking();
 
  private:
+  // Allow tests to access our innards for testing purposes.
+  FRIEND_TEST(FieldTrialTest, Registration);
+  FRIEND_TEST(FieldTrialTest, AbsoluteProbabilities);
+  FRIEND_TEST(FieldTrialTest, RemainingProbability);
+  FRIEND_TEST(FieldTrialTest, FiftyFiftyProbability);
+  FRIEND_TEST(FieldTrialTest, MiddleProbabilities);
+  FRIEND_TEST(FieldTrialTest, OneWinner);
+  FRIEND_TEST(FieldTrialTest, DisableProbability);
+  FRIEND_TEST(FieldTrialTest, Save);
+  FRIEND_TEST(FieldTrialTest, DuplicateRestore);
+  FRIEND_TEST(FieldTrialTest, MakeName);
+
   friend class RefCounted<FieldTrial>;
 
+  // Create a Field Trial that runs forever (expires in 12/31/2099).
+  FieldTrial(const std::string& name, Probability total_probability,
+             const std::string& default_group_name);
+
+  // Determine if the field trial is to be disabled or not based on
+  // expiration time (year, month, day_of_month) and build time of the module.
+  // This method sets disable_field_trial_ to true, if the build time is after
+  // expiration_time_. If disable_field_trial_ is true then the field trial
+  // reverts to the 'default' bucket.
+  void Initialize(const int year, const int month, const int day_of_month);
+
   virtual ~FieldTrial();
 
+  // Get build time.
+  static Time GetBuildTime();
+
   // The name of the field trial, as can be found via the FieldTrialList.
   // This is empty of the trial is not in the experiment.
   const std::string name_;
@@ -133,6 +163,9 @@
   // This is the scaling factor used to adjust supplied probabilities.
   Probability divisor_;
 
+  // The name of the default group.
+  const std::string default_group_name_;
+
   // The randomly selected probability that is used to select a group (or have
   // the instance not participate).  It is the product of divisor_ and a random
   // number between [0, 1).
@@ -144,13 +177,21 @@
   int next_group_number_;
 
   // The pseudo-randomly assigned group number.
-  // This is kNotParticipating if no group has been assigned.
+  // This is kNotFinalized if no group has been assigned.
   int group_;
 
   // A textual name for the randomly selected group, including the Trial name.
   // If this Trial is not a member of an group, this string is empty.
   std::string group_name_;
 
+  // The default value (all remaining probabilities) can be selected after the
+  // expiration_time, which is based on the build time of the module.
+  base::Time expiration_time_;
+
+  // When disable_field_trial_ is true, field trial reverts to the 'default'
+  // bucket.
+  bool disable_field_trial_;
+
   // When benchmarking is enabled, field trials all revert to the 'default'
   // bucket.
   static bool enable_benchmarking_;