Have content/ create and destroy its own threads.

chrome/browser/io_thread.cc

Index: chrome/browser/io_thread.cc
diff --git a/chrome/browser/io_thread.cc b/chrome/browser/io_thread.cc
index b4307f187329a43b887bc58f2518567bcf611037..38ee19c4ed16067f536b731dc51ed053150a476d 100644
--- a/chrome/browser/io_thread.cc
+++ b/chrome/browser/io_thread.cc
@@ -311,7 +311,8 @@ class SystemURLRequestContextGetter : public net::URLRequestContextGetter {
 SystemURLRequestContextGetter::SystemURLRequestContextGetter(
     IOThread* io_thread)
     : io_thread_(io_thread),
-      io_message_loop_proxy_(io_thread->message_loop_proxy()) {
+      io_message_loop_proxy_(
+          BrowserThread::GetMessageLoopProxyForThread(BrowserThread::IO)) {
 }
 
 SystemURLRequestContextGetter::~SystemURLRequestContextGetter() {}
@@ -346,8 +347,7 @@ IOThread::IOThread(
     PrefService* local_state,
     ChromeNetLog* net_log,
     ExtensionEventRouterForwarder* extension_event_router_forwarder)
-    : content::BrowserProcessSubThread(BrowserThread::IO),
-      net_log_(net_log),
+    : net_log_(net_log),
       extension_event_router_forwarder_(extension_event_router_forwarder),
       globals_(NULL),
       sdch_manager_(NULL),
@@ -378,9 +378,6 @@ IOThread::IOThread(
 IOThread::~IOThread() {
   if (pref_proxy_config_tracker_.get())
     pref_proxy_config_tracker_->DetachFromPrefService();
-  // We cannot rely on our base class to stop the thread since we want our
-  // CleanUp function to run.
-  Stop();
   DCHECK(!globals_);
 }
 
@@ -406,9 +403,7 @@ void IOThread::Init() {
   // messages around; it shouldn't be allowed to perform any blocking disk I/O.
   base::ThreadRestrictions::SetIOAllowed(false);
 
-  content::BrowserProcessSubThread::Init();
-
-  DCHECK_EQ(MessageLoop::TYPE_IO, message_loop()->type());
+  DCHECK(BrowserThread::CurrentlyOn(BrowserThread::IO));
 
 #if defined(USE_NSS)
   net::SetMessageLoopForOCSP();
@@ -519,10 +514,6 @@ void IOThread::CleanUp() {
   base::debug::LeakTracker<net::URLRequest>::CheckForLeaks();
 
   base::debug::LeakTracker<SystemURLRequestContextGetter>::CheckForLeaks();
-
-  // This will delete the |notification_service_|.  Make sure it's done after
-  // anything else can reference it.
-  content::BrowserProcessSubThread::CleanUp();
 }
 
 // static
@@ -574,6 +565,11 @@ void IOThread::ClearHostCache() {
     host_cache->clear();
 }
 
+MessageLoop* IOThread::message_loop() const {
+  return BrowserThread::UnsafeGetBrowserThread(
+      BrowserThread::IO)->message_loop();
+}
+
 net::SSLConfigService* IOThread::GetSSLConfigService() {
   return ssl_config_service_manager_->Get();
 }