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

base/metrics/field_trial.cc

 // Copyright (c) 2012 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "base/metrics/field_trial.h"
 
 #include "base/build_time.h"
 #include "base/logging.h"
 #include "base/rand_util.h"
 #include "base/sha1.h"
@@ skipping 152 matching lines @@
   big_string.append(1, kHistogramFieldTrialSeparator);
   return big_string.append(FieldTrialList::FindFullName(trial_name));
 }
 
 // static
 void FieldTrial::EnableBenchmarking() {
   DCHECK_EQ(0u, FieldTrialList::GetFieldTrialCount());
   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) {
   group_ = number;
   if (name.empty())
     StringAppendF(&group_name_, "%d", group_);
   else
     group_name_ = name;
 }
 
@@ skipping 275 matching lines @@
     used_without_global_ = true;
     return;
   }
   AutoLock auto_lock(global_->lock_);
   DCHECK(!global_->PreLockedFind(trial->name()));
   trial->AddRef();
   global_->registered_[trial->name()] = trial;
 }
 
 }  // namespace base