Convert FieldTrialActivated to use mojo.

chrome/browser/field_trial_recorder_impl.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 CHROME_BROWSER_FIELD_TRIAL_RECORDER_IMPL_H_
+#define CHROME_BROWSER_FIELD_TRIAL_RECORDER_IMPL_H_
+
+#include "base/threading/thread_checker.h"
+#include "chrome/common/field_trial_recorder.mojom.h"
+
+class FieldTrialRecorderImpl : public chrome::mojom::FieldTrialRecorder {
+ public:
+  FieldTrialRecorderImpl();
+  ~FieldTrialRecorderImpl() override;
+
+  static void Create(chrome::mojom::FieldTrialRecorderRequest request);
+
+ private:
+  // chrome::mojom::FieldTrialRecorder:
+  void FieldTrialActivated(const std::string& trial_name) override;
+
+  base::ThreadChecker thread_checker_;
+
+  DISALLOW_COPY_AND_ASSIGN(FieldTrialRecorderImpl);
+};
+
+#endif  // CHROME_BROWSER_FIELD_TRIAL_RECORDER_IMPL_H_