Dynamically generate a heading for Extension Docs API pages

chrome/common/extensions/api/events.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": "events",
+    "description": "Use the <code>chrome.event</code> API to notify you when something interesting happens.",
     "compiler_options": {
       "implemented_in": "chrome/browser/extensions/api/declarative/declarative_api.h"
     },
     "internal": true,
     "unprivileged": true,
     "types": [
       {
         "id": "Rule",
         "type": "object",
         "description": "Description of a declarative rule for handling events.",
@@ skipping 280 matching lines @@
                 {"type": "array", "items": {"type": "integer"}, "description": "A pair of integers identiying the start and end (both inclusive) of a port range."}
               ]
             }
           }
         }
       }
     ]
   }
 ]