disable field trials if the build is 30 days or older

base/metrics/field_trial.h

Index: base/metrics/field_trial.h
===================================================================
--- base/metrics/field_trial.h	(revision 70854)
+++ base/metrics/field_trial.h	(working copy)
@@ -112,6 +112,18 @@
   // number is used as the group name.
   std::string group_name() const { return group_name_; }
 
+  // Return true if there is a default group with kAllRemainingProbability.
+  // all_remaining_probability_set_ is set to true when AppendGroup is called
+  // with kAllRemainingProbability as group probability. When MakeName is called
+  // we assert that all_remaining_probability_set_ is set to true.
+  bool all_remaining_probability_set() const {
+    return all_remaining_probability_set_;
+  }
+
+  // Set the usage_timeout from build time of the module to disable Field Trial.
+  void SetUsageTimeout(const base::TimeDelta& usage_timeout);
+  base::TimeDelta usage_timeout() const { return usage_timeout_; }
+
   // Helper function for the most common use: as an argument to specifiy the
   // name of a HISTOGRAM.  Use the original histogram name as the name_prefix.
   static std::string MakeName(const std::string& name_prefix,
@@ -125,6 +137,17 @@
 
   virtual ~FieldTrial();
 
+  // Determine if the field trial is to be disabled or not based on
+  // usage_timeout_, build time of the module and Now(). This method sets
+  // disable_field_trial_ to true, if the difference between build time of the
+  // module and Now() is greater than usage_timeout_. If disable_field_trial_ is
+  // true then the field trial reverts to the 'default' bucket.
+  static bool ShouldFieldTrialBeDisabled(
+      const base::TimeDelta& usage_timeout);
+
+  // 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_;
@@ -151,6 +174,17 @@
   // If this Trial is not a member of an group, this string is empty.
   std::string group_name_;
 
+  // Set to true if there is a default group with kAllRemainingProbability.
+  bool all_remaining_probability_set_;
+
+  // The default value (all remaining probabilities) can be selected after the
+  // usage_timeout, which is based on the build time of the module.
+  base::TimeDelta usage_timeout_;
+
+  // 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_;