Dynamically generate a heading for Extension Docs API pages

chrome/common/extensions/api/file_browser_handler.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":"fileBrowserHandler",
+    "description": "Use the <code>chrome.fileBrowserHandler</code> module to extend the Chrome OS file browser. For example, you can use this API to enable users to upload files to your website.",
     "platforms": ["chromeos"],
     "types": [
       {
         "id": "FileHandlerExecuteEventDetails",
         "type": "object",
         "description": "Event details payload for fileBrowserHandler.onExecute event.",
         "properties": {
           "entries": {
             "type": "array",
             "items": { "type": "any" },
@@ skipping 74 matching lines @@
                   }
                 }
               }
             ]
           }
         ]
       }
     ]
   }
 ]