Add read-only access to POST data for webRequest's onBeforeRequest

chrome/common/extensions/api/web_request_internal.json

 // 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.
 
 [
   {
     "namespace": "webRequestInternal",
     "nodoc": true,
     "internal": true,
     "functions": [
       {
         "name": "addEventListener",
         "type": "function",
         "description": "Used internally to implement the special form of addListener for the webRequest events.",
         "parameters": [
           {"type": "function", "name": "callback"},
           {
             "$ref": "webRequest.RequestFilter",
             "name": "filter",
             "description": "A set of filters that restricts the events that will be sent to this listener."
           },
           {
             "type": "array",
             "optional": true,
             "name": "extraInfoSpec",
             "description": "Array of extra information that should be passed to the listener function.",
             "items": {
               "type": "string",
-              "enum": ["requestHeaders", "responseHeaders", "blocking", "asyncBlocking"]
+              "enum": ["requestHeaders", "responseHeaders", "blocking", "asyncBlocking", "requestPostData"]
             }
           },
           {"type": "string", "name": "eventName"},
           {"type": "string", "name": "subEventName"}
         ]
       },
       {
         "name": "eventHandled",
         "type": "function",
         "description": "Used internally to send a response for a blocked event.",
         "parameters": [
           {"type": "string", "name": "eventName"},
           {"type": "string", "name": "subEventName"},
           {"type": "string", "name": "requestId"},
           {
             "$ref": "webRequest.BlockingResponse",
             "optional": true,
             "name": "response"
           }
         ]
       }
     ]
   }
 ]