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

net/base/net_error_list.h

-// Copyright (c) 2010 The Chromium Authors. All rights reserved.
+// Copyright (c) 2011 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 // This file intentionally does not have header guards, it's included
 // inside a macro to generate enum.
 
 // This file contains the list of network errors.
 
 //
 // Ranges:
@@ skipping 161 matching lines @@
 
 // The SSL server attempted to use a weak ephemeral Diffie-Hellman key.
 NET_ERROR(SSL_WEAK_SERVER_EPHEMERAL_DH_KEY, -129)
 
 // Could not create a connection to the proxy server. An error occurred
 // either in resolving its name, or in connecting a socket to it.
 // Note that this does NOT include failures during the actual "CONNECT" method
 // of an HTTP proxy.
 NET_ERROR(PROXY_CONNECTION_FAILED, -130)
 
-// Free: 131
+// A mandatory proxy configuration could not be used. Currently this means
+// that a mandatory PAC script could not be fetched, parsed or executed.
+NET_ERROR(MANDATORY_PROXY_CONFIGURATION_FAILED, -131)
 
 // We detected an ESET product intercepting our HTTPS connections. Since these
 // products are False Start intolerant, we return this error so that we can
 // give the user a helpful error message rather than have the connection hang.
 NET_ERROR(ESET_ANTI_VIRUS_SSL_INTERCEPTION, -132)
 
 // We've hit the max socket limit for the socket pool while preconnecting.  We
 // don't bother trying to preconnect more sockets.
 NET_ERROR(PRECONNECT_MAX_SOCKET_LIMIT, -133)
 
@@ skipping 328 matching lines @@
 // Import failed - certificate already exists in database.
 // Note it's a little weird this is an error but reimporting a PKCS12 is ok
 // (no-op).  That's how Mozilla does it, though.
 NET_ERROR(IMPORT_CERT_ALREADY_EXISTS, -704)
 
 // CA import failed due to some other error.
 NET_ERROR(IMPORT_CA_CERT_FAILED, -705)
 
 // Server certificate import failed due to some internal error.
 NET_ERROR(IMPORT_SERVER_CERT_FAILED, -706)