Dynamically generate a heading for Extension Docs API pages

chrome/common/extensions/api/types.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": "types",
+    "description": "The <code>chrome.types</code> module contains type declarations for Chrome. Currently this comprises only a prototype for giving other modules access to manage Chrome browser settings. This prototype is used, for example, for $ref:proxy.settings.",
     "types": [
       {
         "id": "ChromeSetting",
         "type": "object",
         "js_module": "ChromeSetting",
         "customBindings": "ChromeSetting",
         "description": "An interface which allows access to a Chrome browser setting.",
         "functions": [
           {
             "name": "get",
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                   }
                 }
               }
             ]
           }
         ]
       }
     ]
   }
 ]