Dynamically generate a heading for Extension Docs API pages

chrome/common/extensions/api/app_runtime.idl

 // 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.
 
+// Use the <code>chrome.app.runtime</code> module to manage the app lifecycle.
+// The app runtime manages app installation, controls the event page, and can
+// shut down the app at anytime.
+
+[availability=23]
 namespace app.runtime {
 
   [inline_doc] dictionary LaunchItem {
     // FileEntry for the file.
     [instanceOf=FileEntry] object entry;
 
     // The MIME type of the file.
     DOMString type;
   };
 
   // Optional data for the launch.
   [inline_doc] dictionary LaunchData {
     // The id of the file handler that the app is being invoked with.
     DOMString? id;
 
     LaunchItem[]? items;
   };
 
   interface Events {
     // Fired when an app is launched from the launcher.
     static void onLaunched(optional LaunchData launchData);
 
     // Fired at Chrome startup to apps that were running when Chrome last shut
     // down.
     static void onRestarted();
   };
 };