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
@@ -34,7 +38,9 @@
     random_(static_cast<Probability>(divisor_ * base::RandDouble())),
     accumulated_group_probability_(0),
     next_group_number_(0),
-    group_(kNotParticipating) {
+    group_(kNotParticipating),
+    duration_after_which_disable_field_trials_(base::TimeDelta::FromDays(30)),
+    disable_field_trails_(false) {
   FieldTrialList::Register(this);
 }
 
@@ -46,8 +52,11 @@
   if (group_probability == kAllRemainingProbability) {
     accumulated_group_probability_ = divisor_;
   } else {
-    if (enable_benchmarking_)
+    if (enable_benchmarking_ ||
+        (base::Time::NowFromSystemTime() - GetBuildTime() >=
+         duration_after_which_disable_field_trials_))
       group_probability = 0;
+
     accumulated_group_probability_ += group_probability;
   }
   DCHECK(accumulated_group_probability_ <= divisor_);
@@ -76,6 +85,18 @@
   enable_benchmarking_ = true;
 }
 
+// static
+Time FieldTrial::GetBuildTime() {
+  static Time integral_build_time;
+  if (integral_build_time.is_null()) {
+    const char* kDateTime = __DATE__ " " __TIME__ " GMT";

[jar (doing other things), 2011/01/09 07:00:04]

caveat: This is OK.... but we should be sure our tests use GMT as well, or we'll
probably fail when we run in certain time zones.  I messed up some related
code... and so I'm now extra wary of his issue.

[rtenneti, 2011/01/09 23:16:42]

Done.

+    bool result = Time::FromString(ASCIIToWide(kDateTime).c_str(),
+                                   &integral_build_time);
+    DCHECK(result);
+  }
+  return integral_build_time;
+}
+
 FieldTrial::~FieldTrial() {}
 
 //------------------------------------------------------------------------------