Move VariationsParamAssociator to base

base/metrics/field_trial_param_associator.h

+// Copyright 2016 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 BASE_METRICS_FIELD_TRIAL_PARAM_ASSOCIATOR_H_
+#define BASE_METRICS_FIELD_TRIAL_PARAM_ASSOCIATOR_H_
+
+#include <map>
+#include <string>
+#include <utility>
+
+#include "base/base_export.h"
+#include "base/memory/singleton.h"
+#include "base/synchronization/lock.h"
+
+namespace base {
+
+// Keeps track of the parameters of all field trials and ensures access to them
+// is thread-safe.
+class BASE_EXPORT FieldTrialParamAssociator {
+ public:
+  FieldTrialParamAssociator();
+  ~FieldTrialParamAssociator();
+
+  // Key-value mapping type for field trial parameters.
+  typedef std::map<std::string, std::string> FieldTrialParams;
+
+  // Retrieve the singleton.
+  static FieldTrialParamAssociator* GetInstance();
+
+  // Sets parameters for the given field trial name and group.
+  bool AssociateFieldTrialParams(const std::string& trial_name,
+                                 const std::string& group_name,
+                                 const FieldTrialParams& params);
+
+  // Gets the parameters for a field trial and its chosen group.
+  bool GetFieldTrialParams(const std::string& trial_name,
+                           FieldTrialParams* params);
+
+  // Clears the internal field_trial_params_ mapping.
+  void ClearAllParamsForTesting();
+
+ private:
+  friend struct DefaultSingletonTraits<FieldTrialParamAssociator>;
+
+  // (field_trial_name, field_trial_group)
+  typedef std::pair<std::string, std::string> FieldTrialKey;
+
+  Lock lock_;
+  std::map<FieldTrialKey, FieldTrialParams> field_trial_params_;
+
+  DISALLOW_COPY_AND_ASSIGN(FieldTrialParamAssociator);
+};
+
+}  // namespace base
+
+#endif  // BASE_METRICS_FIELD_TRIAL_PARAM_ASSOCIATOR_H_