Dynamically generate a heading for Extension Docs API pages

chrome/common/extensions/api/page_action.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": "pageAction",
+    "description": "Use page actions to put icons inside the address bar. Page actions represent actions that can be taken on the current page, but that aren't applicable to all pages.",
     "dependencies": [ "tabs" ],
     "types": [
       {
         "id": "ImageDataType",
         "type": "object",
         "isInstanceOf": "ImageData",
         "additionalProperties": { "type": "any" },
         "description": "Pixel data for an image. Must be an ImageData object (for example, from a <code>canvas</code> element)."
       }
     ],
@@ skipping 164 matching lines @@
         "parameters": [
           {
             "name": "tab",
             "$ref": "tabs.Tab"
           }
         ]
       }
     ]
   }
 ]