Implement A/B experiment for anti-DDoS.

chrome/browser/trials/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/throttling_trial.h"
+
+#include "base/metrics/field_trial.h"
+#include "chrome/browser/prefs/pref_service.h"
+#include "chrome/common/pref_names.h"
+
+namespace throttling_trial {
+
+void CreateTrial(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;
+  // After June 30, 2011 builds, the trial will always be in default group.
+  scoped_refptr<base::FieldTrial> trial(new base::FieldTrial(
+      "ThrottlingEnabled", kTotalProbability, "Default", 2011, 6, 30));

[yzshen1, 2011/06/08 00:56:51]

[out of curiosity]
June 30, 2011 means this will only stay in Dev and Canary builds, right? How
many users are expected to participate in this experiment?

[Jói, 2011/06/08 16:44:47]

Correct, this is just 5% of the dev channel for now.  Depending on the results,
I may tweak things and extend the experiment, or extend it to a larger audience
or just turn the feature on by default.

+  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);
+  }
+}
+
+}  // namespace throttling_trial