Implement URLRequestBackoffManager for managing Backoff headers

net/base/net_error_list.h

 // Copyright (c) 2012 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 values.
 
 // This file contains the list of network errors.
 
 //
@@ skipping 624 matching lines @@
 NET_ERROR(PROXY_HTTP_1_1_REQUIRED, -366)
 
 // The PAC script terminated fatally and must be reloaded.
 NET_ERROR(PAC_SCRIPT_TERMINATED, -367)
 
 // The certificate offered by the alternative server is not valid for the
 // origin, a violation of HTTP Alternative Services specification Section 2.1,
 // https://tools.ietf.org/id/draft-ietf-httpbis-alt-svc-06.html#host_auth.
 NET_ERROR(ALTERNATIVE_CERT_NOT_VALID_FOR_ORIGIN, -368)
 
+// Request is throttled because of a Backoff header.
+// See: crbug.com/486891.
+NET_ERROR(TEMPORARY_BACKOFF, -369)
+
 // The cache does not have the requested entry.
 NET_ERROR(CACHE_MISS, -400)
 
 // Unable to read from the disk cache.
 NET_ERROR(CACHE_READ_FAILURE, -401)
 
 // Unable to write to the disk cache.
 NET_ERROR(CACHE_WRITE_FAILURE, -402)
 
 // The operation is not supported for this entry.
@@ skipping 141 matching lines @@
 NET_ERROR(DNS_TIMED_OUT, -803)
 
 // The entry was not found in cache, for cache-only lookups.
 NET_ERROR(DNS_CACHE_MISS, -804)
 
 // Suffix search list rules prevent resolution of the given host name.
 NET_ERROR(DNS_SEARCH_EMPTY, -805)
 
 // Failed to sort addresses according to RFC3484.
 NET_ERROR(DNS_SORT_ERROR, -806)