Add the capability to run multiple proxy PAC scripts in parallel....

net/base/host_resolver.h

Index: net/base/host_resolver.h
===================================================================
--- net/base/host_resolver.h	(revision 51914)
+++ net/base/host_resolver.h	(working copy)
@@ -177,6 +177,9 @@
   // additional functionality on the about:net-internals page.
   virtual HostResolverImpl* GetAsHostResolverImpl() { return NULL; }
 
+  // Does additional cleanup prior to destruction.
+  virtual void Shutdown() {}
+
  protected:
   friend class base::RefCounted<HostResolver>;