Add a constraint on how many requests can be outstanding for any given render (browser-side).

net/base/net_error_list.h

 // Copyright (c) 2006-2008 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 contains the list of network errors.
 
 // An asynchronous IO operation is not yet complete.  This usually does not
 // indicate a fatal error.  Typically this error will be generated as a
 // notification to wait for some external notification that the IO operation
 // finally completed.
@@ skipping 23 matching lines @@
 // An unexpected error.  This may be caused by a programming mistake or an
 // invalid assumption.
 NET_ERROR(UNEXPECTED, -9)
 
 // Permission to access a resource was denied.
 NET_ERROR(ACCESS_DENIED, -10)
 
 // The operation failed because of unimplemented functionality.
 NET_ERROR(NOT_IMPLEMENTED, -11)
 
+// There were not enough resources to complete the operation.
+NET_ERROR(INSUFFICIENT_RESOURCES, -12)
+
 // A connection was closed (corresponding to a TCP FIN).
 NET_ERROR(CONNECTION_CLOSED, -100)
 
 // A connection was reset (corresponding to a TCP RST).
 NET_ERROR(CONNECTION_RESET, -101)
 
 // A connection attempt was refused.
 NET_ERROR(CONNECTION_REFUSED, -102)
 
 // A connection timed out as a result of not receiving an ACK for data sent.
@@ skipping 169 matching lines @@
     
 // The PAC requested by HTTP did not have a valid status code (non-200).
 NET_ERROR(PAC_STATUS_NOT_OK, -326)
 
 // The cache does not have the requested entry.
 NET_ERROR(CACHE_MISS, -400)
 
 // The server's response was insecure (e.g. there was a cert error).
 NET_ERROR(INSECURE_RESPONSE, -501)