Add unit tests target to GN build.

build/json_schema_api.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.
 
 # Defines a static library corresponding to the output of schema compiler tools
 # over a set of extensions API schemas (IDL or JSON format.) The library target
 # has implicit hard dependencies on all schema files listed by the invoker and
 # is itself a hard dependency.
 #
 # Invocations of this template may use the following variables:
@@ skipping 95 matching lines @@
         "{{source}}",
         "--root=" + rebase_path("//", root_build_dir),
         "--destdir=" + rebase_path(root_gen_dir, root_build_dir),
         "--namespace=$root_namespace",
         "--generator=cpp",
         "--include-rules=$schema_include_rules",
       ]
 
       if (defined(invoker.visibility)) {
         # If visibility is restricted, add our own target to it.
-        visibility = [
-          invoker.visibility,
-          target_visibility,
-        ]
+        visibility = invoker.visibility + target_visibility
       }
     }
   }
 
   if (bundle) {
     uncompiled_sources = []
     if (defined(invoker.uncompiled_sources)) {
       uncompiled_sources = invoker.uncompiled_sources
     }
 
@@ skipping 74 matching lines @@
     public_configs = [ ":$generated_config_name" ]
 
     if (defined(invoker.visibility)) {
       visibility = invoker.visibility
     }
     if (defined(invoker.output_name)) {
       output_name = invoker.output_name
     }
   }
 }