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")
+
 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",
     "app_window_contents.h",
     "app_window_geometry_cache.cc",
     "app_window_geometry_cache.h",
     "app_window_registry.cc",
     "app_window_registry.h",
     "native_app_window.h",
     "size_constraints.cc",
     "size_constraints.h",
   ]
 
   configs += [
     # 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",
   ]
+
+  if (enable_extensions) {
+    deps += [
+      "//extensions:extensions_browser_resources",
+      "//extensions/strings",
+    ]
+  }
 }