Don't cache the IO thread in the MetricsService

chrome/browser/metrics/metrics_service.h

 // Copyright (c) 2012 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.
 
 // This file defines a service that collects information about the user
 // experience in order to help improve future versions of the app.
 
 #ifndef CHROME_BROWSER_METRICS_METRICS_SERVICE_H_
 #define CHROME_BROWSER_METRICS_METRICS_SERVICE_H_
 #pragma once
 
 #include <map>
 #include <string>
 #include <vector>
 
 #include "base/basictypes.h"
 #include "base/gtest_prod_util.h"
 #include "base/memory/weak_ptr.h"
 #include "base/memory/scoped_ptr.h"
 #include "base/memory/weak_ptr.h"
 #include "base/process_util.h"
-#include "chrome/browser/io_thread.h"
 #include "chrome/common/metrics/metrics_service_base.h"
 #include "content/public/common/process_type.h"
 #include "content/public/common/url_fetcher_delegate.h"
 #include "content/public/browser/notification_observer.h"
 #include "content/public/browser/notification_registrar.h"
 
 #if defined(OS_CHROMEOS)
 #include "chrome/browser/chromeos/external_metrics.h"
 #endif
 
@@ skipping 328 matching lines @@
   // The URLs for the XML and protobuf metrics servers.
   string16 server_url_xml_;
   string16 server_url_proto_;
 
   // The TCP/UDP echo server to collect network connectivity stats.
   std::string network_stats_server_;
 
   // The HTTP pipelining test server.
   std::string http_pipelining_test_server_;
 
-  // The IOThread for accessing global HostResolver to resolve
-  // network_stats_server_ host. |io_thread_| is accessed on IO thread and it is
-  // safe to access it on IO thread.
-  IOThread* io_thread_;
-
   // The identifier that's sent to the server with the log reports.
   std::string client_id_;
 
   // Whether the MetricsService object has received any notifications since
   // the last time a transmission was sent.
   bool idle_since_last_transmission_;
 
   // A number that identifies the how many times the app has been launched.
   int session_id_;
 
@@ skipping 52 matching lines @@
   friend bool prerender::IsOmniboxEnabled(Profile* profile);
   friend class extensions::ExtensionDownloader;
 
   // Returns true if prefs::kMetricsReportingEnabled is set.
   static bool IsMetricsReportingEnabled();
 
   DISALLOW_IMPLICIT_CONSTRUCTORS(MetricsServiceHelper);
 };
 
 #endif  // CHROME_BROWSER_METRICS_METRICS_SERVICE_H_