Introduce MetricsServiceClient and ChromeMetricsServiceClient.

components/metrics/metrics_service_client.cc

Index: components/metrics/metrics_service_client.cc
===================================================================
--- components/metrics/metrics_service_client.cc	(revision 0)
+++ components/metrics/metrics_service_client.cc	(working copy)
@@ -0,0 +1,11 @@
+// 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.
+
+#include "chrome/browser/metrics/chrome_metrics_service_client.h"
+
+MetricsServiceClient::MetricsServiceClient() {
+}
+
+virtual MetricsServiceClient::~MetricsServiceClient() {
+}