Dynamically generate a heading for Extension Docs API pages

chrome/common/extensions/api/runtime.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": "runtime",
+    "description": "Use the <code>chrome.runtime</code> module to retrieve the background page, return details about the manifest, and listen for and respond to events in the app or extension lifecycle.",
     "dependencies": [ "events", "tabs" ],
     "documentation_permissions_required": ["runtime"],
     "types": [
       {
         "id": "Port",
         "type": "object",
         "description": "An object which allows two way communication with other pages.",
         "properties": {
           "name": {"type": "string"},
           "disconnect": { "type": "function" },
@@ skipping 345 matching lines @@
           "optional": "true",
           "description": "Return true from the event listener if you wish to call <code>sendResponse</code> after the event listener returns."
         }
       }
 
 
 
     ]
   }
 ]