Added a SetForced method to allow forcing a new set of group bucketting.

base/metrics/field_trial.cc

Index: base/metrics/field_trial.cc
diff --git a/base/metrics/field_trial.cc b/base/metrics/field_trial.cc
index 245f2bf02a6a6e07c4ff0f625c91397f2c04a657..c0e31933550e1b4863d2f12ccfb6a164e1233640 100644
--- a/base/metrics/field_trial.cc
+++ b/base/metrics/field_trial.cc
@@ -170,6 +170,18 @@ void FieldTrial::EnableBenchmarking() {
   enable_benchmarking_ = true;
 }
 
+void FieldTrial::SetForced() {
+  DCHECK(!forced_);
+  // Explicit forcing should only be for cases where we dynamically want to
+  // change the bucketting into groups, so there must have been at least one

[jar (doing other things), 2012/05/05 00:32:26]

I'm not clear what "change the buketting into groups" means.

It is also pretty unclear to me what et means to set forced_ after the fact,
given that we've presumably returned (possibly) something else during the
AppendGroup processing.

[MAD, 2012/05/07 13:48:09]

Done.

+  // non-default group appended.
+  DCHECK_GT(next_group_number_, kDefaultGroupNumber + 1);
+
+  // And we must finalize the group choice before we mark ourselves as forced.
+  group();
+  forced_ = true;
+}
+
 FieldTrial::~FieldTrial() {}
 
 void FieldTrial::SetGroupChoice(const std::string& name, int number) {