Dynamically generate a heading for Extension Docs API pages

chrome/common/extensions/api/app_runtime.idl

Index: chrome/common/extensions/api/app_runtime.idl
diff --git a/chrome/common/extensions/api/app_runtime.idl b/chrome/common/extensions/api/app_runtime.idl
index 391adaa80b9393334939fb27f8af9ef7c0529b68..ef93d2d4df1735d7ab0fdde6676ac8d23ef98827 100644
--- a/chrome/common/extensions/api/app_runtime.idl
+++ b/chrome/common/extensions/api/app_runtime.idl
@@ -2,6 +2,11 @@
 // 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 {