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 5f6cbf2d5e813d3d70643e26db64479d03f267cd..b6851859214c3db2a7e6fc10287d0ba2f79f6e1e 100644
--- a/net/proxy/proxy_service.h
+++ b/net/proxy/proxy_service.h
@@ -328,6 +328,10 @@ class ProxyService : public NetworkChangeNotifier::IPAddressObserver,
 
   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_;