Convert GN visibility variables to lists.

mojo/environment/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.
 
 # GYP version: mojo_base.gyp:mojo_environment_chromium
 source_set("chromium") {
   output_name = "mojo_environment_chromium"
 
   sources = [
     "environment.cc",
     # TODO(vtl): This is kind of ugly. (See TODO in logging.h.)
     "../public/cpp/environment/logging.h",
     "../public/cpp/environment/lib/logging.cc",
   ]
 
   deps = [
     ":chromium_impl",
   ]
 
   forward_dependent_configs_from = [
     ":chromium_impl",
   ]
 }
 
 # GYP version: mojo_base.gyp:mojo_environment_chromium_impl
 component("chromium_impl") {
   output_name = "mojo_environment_impl"
-  visibility = "//mojo/*"
+  visibility = [ "//mojo/*" ]
 
   sources = [
     "default_async_waiter_impl.cc",
     "default_async_waiter_impl.h",
     "default_logger_impl.cc",
     "default_logger_impl.h",
   ]
 
   defines = [
     "MOJO_ENVIRONMENT_IMPL_IMPLEMENTATION",
   ]
 
   deps = [
     "//base",
     "//base/third_party/dynamic_annotations",
     "//mojo/common",
   ]
 }