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

components/guest_view/renderer/BUILD.gn

Index: components/guest_view/renderer/BUILD.gn
diff --git a/components/guest_view/renderer/BUILD.gn b/components/guest_view/renderer/BUILD.gn
index 479bdef0febb40725d14093cec5cd01275fa2e5c..f3d79c79a8b6649d28f5d9a7145259e056e1c1ad 100644
--- a/components/guest_view/renderer/BUILD.gn
+++ b/components/guest_view/renderer/BUILD.gn
@@ -2,9 +2,11 @@
 # 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 = [