Add a ProxyScriptFetcher class for doing asynch downloads of PAC scripts....

net/base/load_flags.h

Index: net/base/load_flags.h
===================================================================
--- net/base/load_flags.h	(revision 6694)
+++ net/base/load_flags.h	(working copy)
@@ -64,6 +64,10 @@
   // An SDCH dictionary was advertised, and an SDCH encoded response is
   // possible.
   LOAD_SDCH_DICTIONARY_ADVERTISED = 1 << 14,
+
+  // Do not resolve proxies. This override is used when downloading PAC files
+  // to avoid having a circular dependency.
+  LOAD_BYPASS_PROXY = 1 << 15,
 };
 
 }  // namespace net