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, as described in detail in <a href='messaging.html'>Message Passing</a>.",
     "compiler_options": {
       "implemented_in": "chrome/browser/extensions/api/module/module.h"
     },
     "types": [
       {
         "id": "MessageSender",
         "type": "object",
         "description": "An object containing information about the script context that sent a message or request.",
         "properties": {
           "tab": {"$ref": "tabs.Tab", "optional": true, "description":"This property will <b>only</b> be present when the connection was opened from a tab or content script."},
@@ skipping 197 matching lines @@
         "description": "Deprecated: please use onMessageExternal.",
         "parameters": [
           {"name": "request", "type": "any", "description": "The request sent by the calling script."},
           {"name": "sender", "$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." }
         ]
       }
     ]
   }
 ]