Add a new priority level, THROTTLED, below IDLE.

net/base/request_priority.cc

 // Copyright (c) 2013 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.
 
 #include "net/base/request_priority.h"
 
 #include "base/logging.h"
 
 namespace net {
 
 const char* RequestPriorityToString(RequestPriority priority) {
   switch (priority) {
+    case THROTTLED:
+      return "THROTTLED";
     case IDLE:
       return "IDLE";
     case LOWEST:
       return "LOWEST";
     case LOW:
       return "LOW";
     case MEDIUM:
       return "MEDIUM";
     case HIGHEST:
       return "HIGHEST";
   }
   NOTREACHED();
   return "UNKNOWN_PRIORITY";
 }
 
 }  // namespace net