Add always-on-top property to app windows

chrome/common/extensions/api/_api_features.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.
 
 // See c/c/e/features/* to understand this file, in particular feature.h,
 // simple_feature.h, and base_feature_provider.h.
 
 {
   "activityLogPrivate": {
     "dependencies": ["permission:activityLogPrivate"],
@@ skipping 26 matching lines @@
     "noparent": true,
     "contexts": ["blessed_extension"],
     "dependencies": ["permission:app.window"]
   },
   "app.currentWindowInternal": {
     "noparent": true,
     "internal": true,
     "channel": "stable",
     "contexts": ["blessed_extension", "unblessed_extension", "content_script"]
   },
+  "app.currentWindowInternal.setAlwaysOnTop": {
+    "channel": "dev",
+    "contexts": ["blessed_extension", "unblessed_extension", "content_script"]
+  },
   "app.getDetails": {
     "contexts": ["blessed_extension", "unblessed_extension", "content_script"],
     "matches": []
   },
   "app.getDetailsForFrame": {
     "contexts": ["blessed_extension", "unblessed_extension", "content_script"],
     "matches": []
   },
   "app.getIsInstalled": {
     "contexts": ["blessed_extension", "unblessed_extension", "content_script"],
@@ skipping 601 matching lines @@
     "internal": true,
     "channel": "stable",
     "dependencies": ["permission:webview"],
     "contexts": ["blessed_extension"]
   },
   "windows": {
     "dependencies": ["api:tabs"],
     "contexts": ["blessed_extension"]
   }
 }