Pass MetricsServiceClient into MetricsService, and create a simple stubbed TestMetricsServiceClient…

chrome/browser/metrics/chrome_metrics_service_client.h

 // Copyright 2014 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_METRICS_CHROME_METRICS_SERVICE_CLIENT_H_
 #define CHROME_BROWSER_METRICS_CHROME_METRICS_SERVICE_CLIENT_H_
 
 #include <string>
 
 #include "base/basictypes.h"
 #include "components/metrics/metrics_service_client.h"
 
 // ChromeMetricsServiceClient provides an implementation of MetricsServiceClient
 // that depends on chrome/.
-class ChromeMetricsServiceClient : metrics::MetricsServiceClient {
+class ChromeMetricsServiceClient : public metrics::MetricsServiceClient {
  public:
   ChromeMetricsServiceClient();
   virtual ~ChromeMetricsServiceClient();
 
   // metrics::MetricsServiceClient:
   virtual void SetClientID(const std::string& client_id) OVERRIDE;
   virtual bool IsOffTheRecordSessionActive() OVERRIDE;
   virtual std::string GetApplicationLocale() OVERRIDE;
   virtual bool GetBrand(std::string* brand_code) OVERRIDE;
   virtual metrics::SystemProfileProto::Channel GetChannel() OVERRIDE;
   virtual std::string GetVersionString() OVERRIDE;
 
  private:
   DISALLOW_COPY_AND_ASSIGN(ChromeMetricsServiceClient);
 };
 
 #endif  // CHROME_BROWSER_METRICS_CHROME_METRICS_SERVICE_CLIENT_H_