Convert GN visibility variables to lists.

third_party/dom_distiller_js/BUILD.gn

 # Copyright 2014 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("//third_party/protobuf/proto_library.gni")
 
 config("dependent_config") {
   include_dirs = [ "//third_party/dom_distiller_js/package/proto_gen" ]
 }
 
 source_set("proto") {
   deps = [ ":dom_distiller_proto" ]
   direct_dependent_configs = [ ":dependent_config" ]
   forward_dependent_configs_from = [ ":dom_distiller_proto" ]
 }
 
 proto_library("dom_distiller_proto") {
-  visibility = ":*"
+  visibility = [ ":*" ]
   sources = [ "package/proto/dom_distiller.proto" ]
   proto_out_dir = "third_party/dom_distiller_js"
 }