Allow generation of a chromium outdirs when enable_extensions=false

extensions/browser/guest_view/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("guest_view") {
   sources = [
     "extensions_guest_view_manager_delegate.cc",
     "extensions_guest_view_manager_delegate.h",
     "extensions_guest_view_message_filter.cc",
     "extensions_guest_view_message_filter.h",
     "guest_view_events.cc",
     "guest_view_events.h",
   ]
 
   public_deps = [
     "//extensions/browser/guest_view/app_view",
     "//extensions/browser/guest_view/extension_options",
     "//extensions/browser/guest_view/extension_view",
     "//extensions/browser/guest_view/extension_view/whitelist",
     "//extensions/browser/guest_view/mime_handler_view",
     "//extensions/browser/guest_view/web_view",
     "//extensions/browser/guest_view/web_view/web_ui",
   ]
 
   deps = [
     "//components/browsing_data/content",
     "//components/guest_view/browser",
     "//content/public/common",
   ]
 }