Make ui gn check pass. Misc GN build improvements.

extensions/generated_extensions_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 91 matching lines @@
         "$target_gen_dir/{{source_name_part}}.cc",
         "$target_gen_dir/{{source_name_part}}.h",
       ]
       args = [
         "{{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" ]
-      visibility = target_visibility
+
+      if (defined(invoker.visibility)) {
+        # If visibility is restricted, add our own target to it.
+        visibility = [ invoker.visibility, target_visibility ]
+      }
     }
   }
 
   if (bundle) {
     uncompiled_sources = []
     if (defined(invoker.uncompiled_sources)) {
      uncompiled_sources = invoker.uncompiled_sources
     }
 
     bundle_generator_schema_name = target_name + "_bundle_generator_schema"
@@ skipping 74 matching lines @@
     direct_dependent_configs = [ ":$generated_config_name" ]
 
     if (defined(invoker.visibility)) {
       visibility = invoker.visibility
     }
     if (defined(invoker.output_name)) {
       output_name = invoker.output_name
     }
   }
 }