Move active field trial API to variations component.

components/variations/active_field_trials.h

Index: components/variations/active_field_trials.h
===================================================================
--- components/variations/active_field_trials.h	(revision 0)
+++ components/variations/active_field_trials.h	(working copy)
@@ -0,0 +1,64 @@
+// Copyright 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.
+
+#ifndef COMPONENTS_VARIATIONS_ACTIVE_FIELD_TRIALS_H_
+#define COMPONENTS_VARIATIONS_ACTIVE_FIELD_TRIALS_H_
+
+#include <string>
+
+#include "base/basictypes.h"
+#include "base/metrics/field_trial.h"
+
+namespace chrome_variations {

[Ilya Sherman, 2014/05/19 12:29:42]

nit: Please update the namespace.

[Alexei Svitkine (slow), 2014/05/19 12:50:47]

Done.

+
+// The Unique ID of a trial and its active group, where the name and group
+// identifiers are hashes of the trial and group name strings.
+struct ActiveGroupId {
+  uint32 name;
+  uint32 group;
+};
+
+// Returns an ActiveGroupId struct for the given trial and group names.
+ActiveGroupId MakeActiveGroupId(const std::string& trial_name,
+                                const std::string& group_name);
+
+// We need to supply a Compare class for templates since ActiveGroupId is a
+// user-defined type.
+struct ActiveGroupIdCompare {
+  bool operator() (const ActiveGroupId& lhs, const ActiveGroupId& rhs) const {
+    // The group and name fields are just SHA-1 Hashes, so we just need to treat
+    // them as IDs and do a less-than comparison. We test group first, since
+    // name is more likely to collide.
+    if (lhs.group != rhs.group)
+      return lhs.group < rhs.group;
+    return lhs.name < rhs.name;
+  }
+};

[Ilya Sherman, 2014/05/19 12:29:42]

Can this be moved into the variations_associated_data implementation file?

[Alexei Svitkine (slow), 2014/05/19 12:50:47]

Unfortunately no, because it's used in the GetFieldTrialActiveGroups TEST.

+
+// Fills the supplied vector |name_group_ids| (which must be empty when called)
+// with unique ActiveGroupIds for each Field Trial that has a chosen group.
+// Field Trials for which a group has not been chosen yet are NOT returned in
+// this list.
+void GetFieldTrialActiveGroupIds(std::vector<ActiveGroupId>* name_group_ids);
+
+// Fills the supplied vector |output| (which must be empty when called) with
+// unique string representations of ActiveGroupIds for each Field Trial that
+// has a chosen group. The strings are formatted as "<TrialName>-<GroupName>",
+// with the names as hex strings. Field Trials for which a group has not been
+// chosen yet are NOT returned in this list.
+void GetFieldTrialActiveGroupIdsAsStrings(std::vector<std::string>* output);
+
+// Expose some functions for testing. These functions just wrap functionality
+// that is implemented above.
+namespace testing {
+
+void TestGetFieldTrialActiveGroupIds(
+    const base::FieldTrial::ActiveGroups& active_groups,
+    std::vector<ActiveGroupId>* name_group_ids);
+
+}  // namespace testing
+
+}  // namespace chrome_variations
+
+#endif  // COMPONENTS_VARIATIONS_ACTIVE_FIELD_TRIALS_H_