Have content/ create and destroy its own threads.

chrome/browser/io_thread.h

Index: chrome/browser/io_thread.h
diff --git a/chrome/browser/io_thread.h b/chrome/browser/io_thread.h
index da098396ff7a49838c168e76261d3e7d69055cd8..7df435fd386834247d2458a27d8b5cd8c3c4b33c 100644
--- a/chrome/browser/io_thread.h
+++ b/chrome/browser/io_thread.h
@@ -49,7 +49,10 @@ class URLRequestContextGetter;
 class URLSecurityManager;
 }  // namespace net
 
-class IOThread : public content::BrowserProcessSubThread {
+// Contains state associated with, and primarily used on, the IO
+// thread.  Also acts as a convenience accessor to the Thread object
+// for the IO thread.
+class IOThread {
  public:
   struct Globals {
     Globals();
@@ -115,6 +118,11 @@ class IOThread : public content::BrowserProcessSubThread {
   // called on the IO thread.
   void ClearHostCache();
 
+  // Convenience method similar to base::Thread, giving access to the
+  // actual IO thread.
+  // TODO(joi): Remove this in follow-up changes.
+  MessageLoop* message_loop() const;
+
  protected:
   virtual void Init();
   virtual void CleanUp();