Decouple Metrics Initialization from IO Thread Initialization

chrome/browser/chrome_browser_main.cc

 // 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.
 
 #include "chrome/browser/chrome_browser_main.h"
 
 #include <stddef.h>
 #include <stdint.h>
 
 #include <set>
@@ skipping 1205 matching lines @@
   //   * Near the end of |PreCreateThreads()|: The TaskScheduler needs to be
   //         created before any other threads are (by contract) but it creates
   //         threads itself so instantiating it earlier is also incorrect.
   // To maintain scoping symmetry, if this line is moved, the corresponding
   // shutdown call may also need to be moved.
   task_scheduler_util::InitializeDefaultBrowserTaskScheduler();
 
   SetupMetrics();
 
   // ChromeOS needs ResourceBundle::InitSharedInstance to be called before this.
-  // This also instantiates the IOThread which requests the metrics service and
-  // must be after |SetupMetrics()|.
   browser_process_->PreCreateThreads();
 
   return content::RESULT_CODE_NORMAL_EXIT;
 }
 
 void ChromeBrowserMainParts::ServiceManagerConnectionStarted(
     content::ServiceManagerConnection* connection) {
   for (size_t i = 0; i < chrome_extra_parts_.size(); ++i)
     chrome_extra_parts_[i]->ServiceManagerConnectionStarted(connection);
 }
@@ skipping 854 matching lines @@
   chromeos::CrosSettings::Shutdown();
 #endif  // defined(OS_CHROMEOS)
 #endif  // defined(OS_ANDROID)
 }
 
 // Public members:
 
 void ChromeBrowserMainParts::AddParts(ChromeBrowserMainExtraParts* parts) {
   chrome_extra_parts_.push_back(parts);
 }