Allow generation of a chromium outdirs when enable_extensions=false

extensions/browser/app_window/BUILD.gn

 # Copyright 2016 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.")
+
 source_set("app_window") {
   sources = [
     "app_delegate.h",
     "app_web_contents_helper.cc",
     "app_web_contents_helper.h",
     "app_window.cc",
     "app_window.h",
     "app_window_client.cc",
     "app_window_client.h",
     "app_window_contents.cc",
@@ skipping 11 matching lines @@
     # TODO(jschuh): crbug.com/167187 fix size_t to int truncations.
     "//build/config/compiler:no_size_t_to_int_warning",
   ]
 
   deps = [
     "//content/public/common",
     "//extensions:extensions_browser_resources",
     "//extensions/strings",
   ]
 }