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

components/guest_view/browser/BUILD.gn

Index: components/guest_view/browser/BUILD.gn
diff --git a/components/guest_view/browser/BUILD.gn b/components/guest_view/browser/BUILD.gn
index 6430459a7f0df73c6a106834a3d4aedc9c0a6ff2..96b43908d4117637be6536e626efa33400e8e24b 100644
--- a/components/guest_view/browser/BUILD.gn
+++ b/components/guest_view/browser/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("browser") {
   output_name = "guest_view_browser"