Improve documentation of extension messaging

chrome/common/extensions/api/tabs.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": "tabs",
     "description": "Use the <code>chrome.tabs</code> API to interact with the browser's tab system. You can use this API to create, modify, and rearrange tabs in the browser.",
     "types": [
       { "id": "MutedInfoReason",
@@ skipping 231 matching lines @@
         "type": "function",
         "description": "Sends a single message to the content script(s) in the specified tab, with an optional callback to run when a response is sent back.  The $(ref:runtime.onMessage) event is fired in each content script running in the specified tab for the current extension.",
         "parameters": [
           {
             "type": "integer",
             "name": "tabId",
             "minimum": 0
           },
           {
             "type": "any",
-            "name": "message"
+            "name": "message",
+            "description": "The message to send. This message should be a JSON-ifiable object."
           },
           {
             "type": "object",
             "name": "options",
             "properties": {
               "frameId": {
                 "type": "integer",
                 "optional": true,
                 "minimum": 0,
                 "description": "Send a message to a specific <a href='webNavigation#frame_ids'>frame</a> identified by <code>frameId</code> instead of all frames in the tab."
@@ skipping 914 matching lines @@
             "tabId": {"type": "integer", "minimum": 0},
             "oldZoomFactor": {"type": "number"},
             "newZoomFactor": {"type": "number"},
             "zoomSettings": {"$ref": "ZoomSettings"}
           }
         }]
       }
     ]
   }
 ]