Allow generation of a chromium outdirs when enable_extensions=false

extensions/shell/installer/linux/BUILD.gn

 # Copyright 2017 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.
 
 # TODO(michaelpg): Dedupe with Chrome installer.
 
 import("//build/config/chrome_build.gni")
 import("//build/config/features.gni")
 import("//build/config/sanitizers/sanitizers.gni")
 import("//build/config/sysroot.gni")
 import("//build/util/version.gni")
 import("//chrome/process_version_rc_template.gni")  # For branding_file_path.
 
 assert(is_desktop_linux)
 assert(current_cpu == "x64")
+assert(enable_extensions,
+       "Cannot depend on extensions because enable_extensions=false.")
 
 # The packages list the exact versions of each library used. The versions used
 # on the bots are likely different than those on your workstation, so you'll
 # get a stream of errors like:
 #   < libasound2 (>= 1.0.23)
 #   ---
 #   > libasound2 (>= 1.0.16)
 #
 # To avoid these warnings for testing purposes, do:
 #
@@ skipping 185 matching lines @@
 # Other packages that we support that aren't included in the default "linux"
 # target.
 linux_package("trunk") {
   channel = "trunk"
 }
 if (is_asan) {
   linux_package("asan") {
     channel = "asan"
   }
 }