Move ProxyConfigService construction onto the IO thread.

net/proxy/proxy_config_service.h

 // Copyright (c) 2011 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.
 
 #ifndef NET_PROXY_PROXY_CONFIG_SERVICE_H_
 #define NET_PROXY_PROXY_CONFIG_SERVICE_H_
 
 #include "net/base/net_export.h"
 
 namespace net {
@@ skipping 43 matching lines @@
   virtual ConfigAvailability GetLatestProxyConfig(ProxyConfig* config) = 0;
 
   // ProxyService will call this periodically during periods of activity.
   // It can be used as a signal for polling-based implementations.
   //
   // Note that this is purely used as an optimization -- polling
   // implementations could simply set a global timer that goes off every
   // 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 main thread to indicate now is the time for shutdown work
+  // that must occur on the main thread.  Its also one of the last safe times
+  // to post shutdown tasks to other browser threads.

[Ryan Sleevi, 2012/10/19 17:56:43]

nit: comment layering violation within net/ "to other browser threads".
BrowserThread is a content/ concept. I'd suggest just saying "threads"

From a high-level perspective though, I'm concerned about introducing the idea
of browser/process shutdown into the net/ layer. It would be much nicer if the
shutdown semantics in net/ just focused on the object lifetimes, rather than the
overall process lifetimes. The fact that there is only one PCS per-process - or
whatever other such - shouldn't alter these semantics.

Most importantly, I think it introduces a real design flaw, in that it forces
every ProxyConfigService to consider living on two threads (the Network thread,
where it's created, and the main thread, where this can be called). I'm really
opposed to this, and tried to work very hard during the Android changes to try
and separate out the objects and give them distinct and clear lifetimes.

+  virtual void StartTearDown() {}
 };
 
 }  // namespace net
 
 #endif  // NET_PROXY_PROXY_CONFIG_SERVICE_H_