Convert GN visibility variables to lists.

base/allocator/BUILD.gn

 # Copyright (c) 2013 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("//build/config/allocator.gni")
 
 # Only executables and not libraries should depend on the allocator target;
 # only the application (the final executable) knows what allocator makes sense.
 # This "allocator" meta-target will forward to the default allocator according
 # to the build settings.
@@ skipping 222 matching lines @@
       "//base/third_party/dynamic_annotations",
     ]
 
     if (is_win) {
       ldflags = [ "/ignore:4006:4221" ]
     }
   }
 }  # !is_android
 
 source_set("allocator_extension_thunks") {
-  visibility = "//base/*"
+  visibility = [ "//base/*" ]
   sources = [
     "allocator_extension_thunks.cc",
     "allocator_extension_thunks.h",
   ]
 }