Enable (optional) blocking of webrequests in case a PAC script cannot be fetched or is invalid.

net/proxy/proxy_service.h

Index: net/proxy/proxy_service.h
diff --git a/net/proxy/proxy_service.h b/net/proxy/proxy_service.h
index 814647098d6d145f860ef50e68382bd9cd397156..8e3c620e3967d3ef79ceb808c1a2418c3501a68c 100644
--- a/net/proxy/proxy_service.h
+++ b/net/proxy/proxy_service.h
@@ -330,6 +330,10 @@ class ProxyService : public base::RefCounted<ProxyService>,
 
   State current_state_;
 
+  // Either OK or an ERR_* value indicating that a permanent error (e.g.
+  // failed to fetch the PAC script) prevents proxy resolution.
+  int permanent_error_;
+
   // This is the log where any events generated by |init_proxy_resolver_| are
   // sent to.
   NetLog* net_log_;