Convert GN visibility variables to lists.

tools/generate_library_loader/generate_library_loader.gni

 # 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.
 
 # This template makes a stub for a Linux system library that dynamically loads
 # it at runtime.
 
 # name: Name to use for the value of the --name arg.
 # output_h/output_cc: Names for the generated header/cc file with no dir.
 # header: header file to process. Example: "<foo/bar.h>"
 # functions: List of strings for functions to process.
 # config: (optional) Label of the config generated by pkgconfig.
 # bundled_header: (optional)
 template("generate_library_loader") {
   output_h = "$root_gen_dir/library_loaders/" + invoker.output_h
   output_cc = "$root_gen_dir/library_loaders/" + invoker.output_cc
 
-  action_visibility = ":$target_name"
+  action_visibility = [ ":$target_name" ]
   action("${target_name}_loader") {
     visibility = action_visibility
 
     script = "//tools/generate_library_loader/generate_library_loader.py"
     if (defined(invoker.visibility)) {
       visibility = invoker.visibility
     }
 
     outputs = [ output_h, output_cc ]
 
@@ skipping 16 matching lines @@
   }
 
   source_set(target_name) {
     if (defined(invoker.config)) {
       direct_dependent_configs = [ invoker.config ]
     }
     sources = [ output_h, output_cc ]
     deps = [ ":${target_name}_loader" ]
   }
 }