Revert of Reland: Lazily initialize MessageLoop for faster thread startup

chrome/browser/io_thread.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/io_thread.h"
 
 #include <vector>
 
 #include "base/base64.h"
 #include "base/bind.h"
@@ skipping 590 matching lines @@
 
 net::URLRequestContextGetter* IOThread::system_url_request_context_getter() {
   DCHECK(BrowserThread::CurrentlyOn(BrowserThread::UI));
   if (!system_url_request_context_getter_.get()) {
     InitSystemRequestContext();
   }
   return system_url_request_context_getter_.get();
 }
 
 void IOThread::Init() {
+  // Prefer to use InitAsync unless you need initialization to block
+  // the UI thread
+}
+
+void IOThread::InitAsync() {
   // TODO(erikchen): Remove ScopedTracker below once http://crbug.com/466432
   // is fixed.
   tracked_objects::ScopedTracker tracking_profile1(
       FROM_HERE_WITH_EXPLICIT_FUNCTION("466432 IOThread::InitAsync::Start"));
   TRACE_EVENT0("startup", "IOThread::InitAsync");
   DCHECK(BrowserThread::CurrentlyOn(BrowserThread::IO));
 
 #if defined(USE_NSS_CERTS) || defined(OS_IOS)
   net::SetMessageLoopForNSSHttpIO();
 #endif
@@ skipping 1006 matching lines @@
   net::QuicVersionVector supported_versions = net::QuicSupportedVersions();
   for (size_t i = 0; i < supported_versions.size(); ++i) {
     net::QuicVersion version = supported_versions[i];
     if (net::QuicVersionToString(version) == quic_version) {
       return version;
     }
   }
 
   return net::QUIC_VERSION_UNSUPPORTED;
 }