Dynamically generate a heading for Extension Docs API pages

chrome/common/extensions/api/extension.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": "extension",
+    "description": "The <code>chrome.extension</code> module has utilities that can be used by any extension page. It includes support for exchanging messages between an extension and its content scripts or between extensions.",
     "compiler_options": {
       "implemented_in": "chrome/browser/extensions/api/module/module.h"
     },
     "dependencies": [ "events", "tabs" ],
     "types": [
       {
         "id": "MessageSender",
         "type": "object",
         "description": "An object containing information about the script context that sent a message or request.",
         "properties": {
@@ skipping 189 matching lines @@
         "description": "Deprecated: please use onMessageExternal.",
         "parameters": [
           {"name": "request", "type": "any", "description": "The request sent by the calling script."},
           {"name": "sender", "$ref": "MessageSender" },
           {"name": "sendResponse", "type": "function", "description": "Function to call when you have a response. The argument should be any JSON-ifiable object, or undefined if there is no response." }
         ]
       }
     ]
   }
 ]