Dynamically generate a heading for Extension Docs API pages

chrome/common/extensions/api/font_settings.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": "fontSettings",
+    "description": "The Font Settings API allows you to manage Chrome's font settings.",
     "documentation_permissions_required": ["fontSettings"],
     "types": [
       {
         "id": "FontName",
         "type": "object",
         "description": "Represents a font name.",
         "properties": {
           "fontId": {
             "type": "string",
             "description": "The font ID."
@@ skipping 469 matching lines @@
                 "$ref": "LevelOfControl",
                 "description": "The level of control this extension has over the setting."
               }
             }
           }
         ]
       }
     ]
   }
 ]