Move ProxyConfigService construction onto the IO thread.

net/proxy/proxy_config_service.h

Index: net/proxy/proxy_config_service.h
diff --git a/net/proxy/proxy_config_service.h b/net/proxy/proxy_config_service.h
index 5e14995d0933fe615f8d5b1a0eb1dadb877b938e..d0247973a371307ceb9f8e539366348438075314 100644
--- a/net/proxy/proxy_config_service.h
+++ b/net/proxy/proxy_config_service.h
@@ -61,6 +61,12 @@ class NET_EXPORT ProxyConfigService {
   // X seconds at which point they check for changes. However that has
   // the disadvantage of doing continuous work even during idle periods.
   virtual void OnLazyPoll() {}
+
+
+  // Called on the Glib thread to indicate now is the time for shutdown work
+  // that must occur on the Glib thread.  Its also one of the last safe times
+  // to post shutdown tasks to other browser threads.
+  virtual void StartTearDown() {}
 };
 
 }  // namespace net