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diff --git a/components/variations/synthetic_trials.h b/components/variations/synthetic_trials.h
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+// Copyright 2015 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_SYNTHETIC_TRIALS_H_
+#define COMPONENTS_VARIATIONS_SYNTHETIC_TRIALS_H_
+
+#include <vector>
+
+#include "base/compiler_specific.h"
+#include "base/time/time.h"
+#include "components/variations/active_field_trials.h"
+
+namespace variations {
+
+// A Field Trial and its selected group, which represent a particular
+// Chrome configuration state. For example, the trial name could map to
+// a preference name, and the group name could map to a preference value.
+struct SyntheticTrialGroup {
+ public:
+  SyntheticTrialGroup(uint32_t trial, uint32_t group);
+  ~SyntheticTrialGroup();
+
+  ActiveGroupId id;
+  base::TimeTicks start_time;
+};
+
+// Interface class to observe changes to synthetic trials in MetricsService.
+class SyntheticTrialObserver {
+ public:
+  // Called when the list of synthetic field trial groups has changed.
+  virtual void OnSyntheticTrialsChanged(
+      const std::vector<SyntheticTrialGroup>& groups) = 0;
+
+ protected:
+  virtual ~SyntheticTrialObserver() {}
+};
+
+}  // namespace variations
+
+#endif  // COMPONENTS_VARIATIONS_SYNTHETIC_TRIALS_H_