Allow generation of a chromium outdirs when enable_extensions=false

extensions/browser/updater/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("updater") {
   sources = [
     "extension_cache.h",
     "extension_downloader.cc",
     "extension_downloader.h",
     "extension_downloader_delegate.cc",
     "extension_downloader_delegate.h",
     "extension_downloader_test_delegate.h",
     "manifest_fetch_data.cc",
     "manifest_fetch_data.h",
@@ skipping 18 matching lines @@
   configs += [
     # TODO(jschuh): crbug.com/167187 fix size_t to int truncations.
     "//build/config/compiler:no_size_t_to_int_warning",
   ]
 
   deps = [
     "//extensions/common",
     "//extensions/strings",
   ]
 }