disable field trials if the build is 30 days or older

base/metrics/field_trial_unittest.cc

Index: base/metrics/field_trial_unittest.cc
===================================================================
--- base/metrics/field_trial_unittest.cc	(revision 70854)
+++ base/metrics/field_trial_unittest.cc	(working copy)
@@ -160,6 +160,22 @@
   EXPECT_EQ(trial->group_name(), winner_name);
 }
 
+TEST_F(FieldTrialTest, DisableProbability) {
+  // First create a test that hasn't had a winner yet.
+  const std::string winner = "Winner";
+  const std::string loser = "Loser";
+  scoped_refptr<FieldTrial> trial;
+  std::string name = StringPrintf("trial");
+  trial = new FieldTrial(name, 1000000000);
+  trial->SetUsageTimeout(base::TimeDelta::FromDays(-1));
+  trial->AppendGroup(loser, 999999999);  // 99.9999999% chance of being chosen.
+  // Now add a winner with all remaining probability.
+  trial->AppendGroup(winner, FieldTrial::kAllRemainingProbability);
+
+  // And that winner should ALWAYS win.
+  EXPECT_EQ(winner, trial->group_name());
+}
+
 TEST_F(FieldTrialTest, Save) {
   std::string save_string;