Have content/ create and destroy its own threads.

chrome/browser/chrome_browser_parts_aura.cc

Index: chrome/browser/chrome_browser_parts_aura.cc
diff --git a/chrome/browser/chrome_browser_parts_aura.cc b/chrome/browser/chrome_browser_parts_aura.cc
index 5dbcada6312e5d2ecbdbf9c34b09ddf44f020ec5..7cc2e13900837f88859d64b22a98644d85bddba8 100644
--- a/chrome/browser/chrome_browser_parts_aura.cc
+++ b/chrome/browser/chrome_browser_parts_aura.cc
@@ -30,7 +30,7 @@ void ChromeBrowserPartsAura::PreMainMessageLoopStart() {
 void ChromeBrowserPartsAura::PostMainMessageLoopStart() {
 }
 
-void ChromeBrowserPartsAura::PreMainMessageLoopRun() {
+content::IOThreadDelegate* ChromeBrowserPartsAura::PreMainMessageLoopRun() {
 #if defined(OS_CHROMEOS)
   if (chromeos::system::runtime_environment::IsRunningOnChromeOS())
     aura::Desktop::set_use_fullscreen_host_window(true);
@@ -38,6 +38,7 @@ void ChromeBrowserPartsAura::PreMainMessageLoopRun() {
 
   // Shell takes ownership of ChromeShellDelegate.
   aura_shell::Shell::GetInstance()->SetDelegate(new ChromeShellDelegate);
+  return NULL;
 }
 
 bool ChromeBrowserPartsAura::MainMessageLoopRun(int* result_code) {