Remove references to extensions from //components/guest_view/.

components/guest_view/renderer/BUILD.gn

 # Copyright 2015 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)
+# Currently, GuestViews are only used by extensions, so we have this
+# assert to prevent the accidental building of GuestViews on mobile
+# platforms. If you're now using GuestViews on mobile, go ahead and
+# remove this assert.
+assert(!is_android && !is_ios)
 
 static_library("renderer") {
   sources = [
     "guest_view_container.cc",
     "guest_view_container.h",
     "guest_view_container_dispatcher.cc",
     "guest_view_container_dispatcher.h",
     "guest_view_request.cc",
     "guest_view_request.h",
     "iframe_guest_view_container.cc",
     "iframe_guest_view_container.h",
     "iframe_guest_view_request.cc",
     "iframe_guest_view_request.h",
   ]
 
   deps = [
     "//base",
     "//components/guest_view/common",
     "//content/public/common",
     "//content/public/renderer",
     "//third_party/WebKit/public:blink",
     "//v8",
   ]
 
   public_deps = [
     "//ipc",
   ]
 }