Move uniformity trials to its own file.

chrome/common/metrics/variations/uniformity_field_trials.cc

+// Copyright (c) 2013 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/common/metrics/variations/uniformity_field_trials.h"
+
+#include "base/metrics/field_trial.h"
+#include "base/stringprintf.h"
+#include "chrome/common/metrics/variations/variations_util.h"
+
+namespace {
+
+// Set up a uniformity field trial. |one_time_randomized| indicates if the
+// field trial is one-time randomized or session-randomized. |trial_name_string|
+// must contain a "%d" since the percentage of the group will be inserted in
+// the trial name. |num_trial_groups| must be a divisor of 100 (e.g. 5, 20)
+void SetupSingleUniformityFieldTrial(
+    bool one_time_randomized,
+    const std::string& trial_name_string,
+    const chrome_variations::VariationID trial_base_id,
+    int num_trial_groups) {
+  // Probability per group remains constant for all uniformity trials, what
+  // changes is the probability divisor.
+  static const base::FieldTrial::Probability kProbabilityPerGroup = 1;
+  const std::string kDefaultGroupName = "default";
+  const base::FieldTrial::Probability divisor = num_trial_groups;
+
+  DCHECK_EQ(100 % num_trial_groups, 0);
+  const int group_percent = 100 / num_trial_groups;
+  const std::string trial_name = StringPrintf(trial_name_string.c_str(),
+                                              group_percent);
+
+  DVLOG(1) << "Trial name = " << trial_name;
+
+  scoped_refptr<base::FieldTrial> trial(
+      base::FieldTrialList::FactoryGetFieldTrial(
+          trial_name, divisor, kDefaultGroupName, 2015, 1, 1, NULL));
+  if (one_time_randomized)
+    trial->UseOneTimeRandomization();
+  chrome_variations::AssociateGoogleVariationID(
+      chrome_variations::GOOGLE_WEB_PROPERTIES, trial_name, kDefaultGroupName,
+      trial_base_id);
+  chrome_variations::AssociateGoogleVariationID(
+      chrome_variations::GOOGLE_UPDATE_SERVICE, trial_name, kDefaultGroupName,
+      trial_base_id);
+
+  // Loop starts with group 1 because the field trial automatically creates a
+  // default group, which would be group 0.
+  for (int group_number = 1; group_number < num_trial_groups; ++group_number) {
+    const std::string group_name = StringPrintf("group_%02d", group_number);
+    DVLOG(1) << "    Group name = " << group_name;
+    trial->AppendGroup(group_name, kProbabilityPerGroup);
+    chrome_variations::AssociateGoogleVariationID(
+        chrome_variations::GOOGLE_WEB_PROPERTIES, trial_name, group_name,
+        static_cast<chrome_variations::VariationID>(trial_base_id +
+                                                    group_number));
+    chrome_variations::AssociateGoogleVariationID(
+        chrome_variations::GOOGLE_UPDATE_SERVICE, trial_name, group_name,
+        static_cast<chrome_variations::VariationID>(trial_base_id +
+                                                    group_number));
+  }
+
+  // Now that all groups have been appended, call group() on the trial to
+  // ensure that our trial is registered. This resolves an off-by-one issue
+  // where the default group never gets chosen if we don't "use" the trial.
+  const int chosen_group = trial->group();
+  DVLOG(1) << "Chosen Group: " << chosen_group;
+}
+
+// Setup a 50% uniformity trial for new installs only. This is accomplished by
+// disabling the trial on clients that were installed before a specified date.
+void SetupNewInstallUniformityTrial(const base::Time& install_date) {
+  const base::Time::Exploded kStartDate = {
+    2012, 11, 0, 6,  // Nov 6, 2012
+    0, 0, 0, 0       // 00:00:00.000
+  };
+  scoped_refptr<base::FieldTrial> trial(
+      base::FieldTrialList::FactoryGetFieldTrial(
+          "UMA-New-Install-Uniformity-Trial", 100, "Disabled",
+          2015, 1, 1, NULL));
+  trial->UseOneTimeRandomization();
+  trial->AppendGroup("Control", 50);
+  trial->AppendGroup("Experiment", 50);
+  const base::Time start_date = base::Time::FromLocalExploded(kStartDate);
+  if (install_date < start_date)
+    trial->Disable();
+  else
+    trial->group();
+}
+
+}  // namespace
+
+namespace chrome_variations {
+
+void SetupUniformityFieldTrials(const base::Time& install_date) {
+  // One field trial will be created for each entry in this array. The i'th
+  // field trial will have |trial_sizes[i]| groups in it, including the default
+  // group. Each group will have a probability of 1/|trial_sizes[i]|.
+  const int num_trial_groups[] = { 100, 20, 10, 5, 2 };
+
+  // Declare our variation ID bases along side this array so we can loop over it
+  // and assign the IDs appropriately. So for example, the 1 percent experiments
+  // should have a size of 100 (100/100 = 1).
+  const chrome_variations::VariationID trial_base_ids[] = {
+      chrome_variations::UNIFORMITY_1_PERCENT_BASE,
+      chrome_variations::UNIFORMITY_5_PERCENT_BASE,

[Alexei Svitkine (slow), 2013/02/27 16:24:55]

Nit: Indent 2? Alternatively, indent 4 the kStartDate in the function above.

[SteveT, 2013/02/27 16:33:48]

Haha, I had originally made this indent 2 but then moved it back to 4 because I
didn't want to touch any of the existing code.

But yes, I believe 2 is correct as per a discussion we had in another CL.

+      chrome_variations::UNIFORMITY_10_PERCENT_BASE,
+      chrome_variations::UNIFORMITY_20_PERCENT_BASE,
+      chrome_variations::UNIFORMITY_50_PERCENT_BASE
+  };
+
+  const std::string kOneTimeRandomizedTrialName =
+      "UMA-Uniformity-Trial-%d-Percent";
+  for (size_t i = 0; i < arraysize(num_trial_groups); ++i) {
+    SetupSingleUniformityFieldTrial(true, kOneTimeRandomizedTrialName,
+                                    trial_base_ids[i], num_trial_groups[i]);
+  }
+
+  // Setup a 5% session-randomized uniformity trial.
+  const std::string kSessionRandomizedTrialName =
+      "UMA-Session-Randomized-Uniformity-Trial-%d-Percent";
+  SetupSingleUniformityFieldTrial(false, kSessionRandomizedTrialName,
+      chrome_variations::UNIFORMITY_SESSION_RANDOMIZED_5_PERCENT_BASE, 20);
+
+  SetupNewInstallUniformityTrial(install_date);
+}
+
+}  // namespace chrome_variations