Construct a field trial to see if HIGH or MEDIUM memory model "works better"...

base/field_trial.cc

+// Copyright (c) 2006-2008 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/field_trial.h"
+#include "base/logging.h"
+#include "base/rand_util.h"
+
+//------------------------------------------------------------------------------
+// FieldTrialList methods and members.
+
+// static
+FieldTrialList* FieldTrialList::global_ = NULL;
+
+// static
+int FieldTrialList::constructor_count_ = 0;
+
+FieldTrialList::FieldTrialList()
+  : application_start_time_(Time::Now()) {
+  DCHECK(!constructor_count_);
+  ++constructor_count_;
+  global_ = this;
+}
+
+FieldTrialList::~FieldTrialList() {
+  while (!registered_.empty()) {
+    RegistrationList::iterator it = registered_.begin();
+    it->second->Release();
+    registered_.erase(it->first);
+  }
+  DCHECK(this == global_);
+  global_ = NULL;
+}
+
+// static
+void FieldTrialList::Register(FieldTrial* trial) {
+  DCHECK(global_->CalledOnValidThread());
+  DCHECK(!Find(trial->name()));
+  trial->AddRef();
+  global_->registered_[trial->name()] = trial;
+}
+
+// static
+FieldTrial* FieldTrialList::Find(const std::wstring& name) {
+  DCHECK(global_->CalledOnValidThread());
+  RegistrationList::iterator it = global_->registered_.find(name);
+  if (global_->registered_.end() == it)
+    return NULL;
+  return it->second;
+}
+
+//------------------------------------------------------------------------------
+// FieldTrial methods and members.
+
+FieldTrial::FieldTrial(const std::wstring& name, double probability)
+  : name_(name) {
+  double rand = base::RandDouble();
+  DCHECK(rand >= 0.0  && rand < 1.0);
+  boolean_value_ = rand < probability;
+  FieldTrialList::Register(this);
+}