disable field trials if the build is 30 days or older

base/metrics/field_trial.cc

Index: base/metrics/field_trial.cc
===================================================================
--- base/metrics/field_trial.cc	(revision 70854)
+++ base/metrics/field_trial.cc	(working copy)
@@ -7,7 +7,11 @@
 #include "base/logging.h"
 #include "base/rand_util.h"
 #include "base/stringprintf.h"
+#include "base/utf_string_conversions.h"
 
+using base::Time;
+using base::TimeDelta;
+
 namespace base {
 
 // static
@@ -34,8 +38,11 @@
     random_(static_cast<Probability>(divisor_ * base::RandDouble())),
     accumulated_group_probability_(0),
     next_group_number_(0),
-    group_(kNotParticipating) {
+    group_(kNotParticipating),
+    all_remaining_probability_set_(false),
+    usage_timeout_(base::TimeDelta::FromDays(30)) {
   FieldTrialList::Register(this);
+  disable_field_trial_ = ShouldFieldTrialBeDisabled(usage_timeout_);
 }
 
 int FieldTrial::AppendGroup(const std::string& name,
@@ -45,9 +52,11 @@
          group_probability == kAllRemainingProbability);
   if (group_probability == kAllRemainingProbability) {
     accumulated_group_probability_ = divisor_;
+    all_remaining_probability_set_ = true;
   } else {
-    if (enable_benchmarking_)
+    if (enable_benchmarking_ || disable_field_trial_)
       group_probability = 0;
+
     accumulated_group_probability_ += group_probability;
   }
   DCHECK(accumulated_group_probability_ <= divisor_);
@@ -62,6 +71,11 @@
   return next_group_number_++;
 }
 
+void FieldTrial::SetUsageTimeout(const base::TimeDelta& usage_timeout) {
+  usage_timeout_ = usage_timeout;
+  disable_field_trial_ = ShouldFieldTrialBeDisabled(usage_timeout);
+}
+
 // static
 std::string FieldTrial::MakeName(const std::string& name_prefix,
                                  const std::string& trial_name) {
@@ -76,6 +90,26 @@
   enable_benchmarking_ = true;
 }
 
+// static
+bool FieldTrial::ShouldFieldTrialBeDisabled(
+    const base::TimeDelta& usage_timeout) {
+  if (base::Time::NowFromSystemTime() - GetBuildTime() >= usage_timeout)
+    return true;
+  return false;
+}
+
+// static
+Time FieldTrial::GetBuildTime() {
+  static Time integral_build_time;
+  if (integral_build_time.is_null()) {
+    const char* kDateTime = __DATE__ " " __TIME__;
+    bool result = Time::FromString(ASCIIToWide(kDateTime).c_str(),
+                                   &integral_build_time);
+    DCHECK(result);
+  }
+  return integral_build_time;
+}
+
 FieldTrial::~FieldTrial() {}
 
 //------------------------------------------------------------------------------
@@ -127,8 +161,10 @@
 // static
 std::string FieldTrialList::FindFullName(const std::string& name) {
   FieldTrial* field_trial = Find(name);
-  if (field_trial)
+  if (field_trial) {
+    DCHECK(field_trial->all_remaining_probability_set());
     return field_trial->group_name();
+  }
   return "";
 }
 
@@ -197,7 +233,7 @@
     }
     const int kTotalProbability = 100;
     field_trial = new FieldTrial(name, kTotalProbability);
-    field_trial->AppendGroup(group_name, kTotalProbability);
+    field_trial->AppendGroup(group_name, FieldTrial::kAllRemainingProbability);
   }
   return true;
 }