Reland (3rd try): Lazily initialize MessageLoop for faster thread startup

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 0a306c7c48522c6646d9d6c5767e5cd1c654db0f..e89a41526a186b0bf5ca22e08df28f2b4303d728 100644
--- a/chrome/browser/io_thread.cc
+++ b/chrome/browser/io_thread.cc
@@ -611,11 +611,6 @@ net::URLRequestContextGetter* IOThread::system_url_request_context_getter() {
 }
 
 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(