Allow generation of a chromium outdirs when enable_extensions=false

extensions/components/native_app_window/BUILD.gn

 # Copyright 2014 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.
 
+import("//extensions/features/features.gni")
+
+assert(enable_extensions,
+       "Cannot depend on extensions because enable_extensions=false.")
+
 static_library("native_app_window") {
   sources = [
     "native_app_window_views.cc",
     "native_app_window_views.h",
   ]
 
   deps = [
     "//base",
     "//content/public/browser",
     "//extensions/browser",
     "//extensions/common",
     "//skia",
     "//ui/views",
     "//ui/views/controls/webview",
   ]
 }