Implement A/B experiment for anti-DDoS.

chrome/browser/trials/http_throttling_trial.cc

+// Copyright (c) 2011 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 "chrome/browser/trials/http_throttling_trial.h"
+
+#include "base/metrics/field_trial.h"
+#include "chrome/browser/prefs/pref_service.h"
+#include "chrome/common/pref_names.h"
+
+void CreateHttpThrottlingTrial(PrefService* prefs) {
+  DCHECK(prefs);
+
+  // We only use one-time randomization, meaning each client will be put
+  // in the same group on every startup, so that users do not have a situation
+  // where they are intermittently in the experiment group, and have problems
+  // because of throttling, then turn off their browser to fix the problem,
+  // come back, and cannot figure out why they had problems (because throttling
+  // will most likely by then be turned off).  A lesser concern is that if
+  // we didn't use one-time randomization, users might notice the preference
+  // in about:net-internals toggling from one state to the other.
+  if (!base::FieldTrialList::IsOneTimeRandomizationEnabled())
+    return;
+
+  // Probability for each trial group (the experiment and the control) is 5%.
+  const base::FieldTrial::Probability kEachGroupProbability = 5;
+  const base::FieldTrial::Probability kTotalProbability = 100;
+  // Disable trial a couple of days before M14 branch point.
+  scoped_refptr<base::FieldTrial> trial(new base::FieldTrial(
+      "HttpThrottlingEnabled", kTotalProbability, "Default", 2011, 7, 23));
+  trial->UseOneTimeRandomization();
+
+  // If the user has touched the control for whether throttling is enabled
+  // or not, we only allow the Default group for the trial, and we do not
+  // modify the value of prefs::kHttpThrottlingEnabled.
+  if (prefs->GetBoolean(prefs::kHttpThrottlingMayExperiment)) {
+    int experiment_group =
+        trial->AppendGroup("Experiment", kEachGroupProbability);
+
+    // The behavior for the control group is the same as for the default group.
+    // The point of having the control group is that it's the same size as
+    // the experiment group and selected the same way, so we get an
+    // apples-to-apples comparison of histograms.
+    trial->AppendGroup("Control", kEachGroupProbability);
+
+    prefs->SetBoolean(prefs::kHttpThrottlingEnabled,
+                      trial->group() == experiment_group);
+  }
+}