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

Includes definition of a FieldTrial class to support this.
I have thoughts in my head about how this will eventually
extend to be controllable via UMA (as well as being able
to run tests defined at compile time, as was done in this
example.


r=mbelshe, mmentovai
Review URL: http://codereview.chromium.org/7638

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@3604 0039d316-1c4b-4281-b951-d872f2087c98

1 files changed, 62 insertions, 0 deletions

diff --git a/base/field_trial.cc b/base/field_trial.cc
new file mode 100644
index 0000000..103e539
--- /dev/null
+++ b/base/field_trial.cc
@@ -0,0 +1,62 @@
+// 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);
+}