Adjust the visibility of the standalone targets in the GN build.

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.
 
 import("//build/config/android/config.gni")
 import("//build/config/arm.gni")
 import("//build/config/mips.gni")
 
 # Because standalone V8 builds are not supported, assume this is part of a
 # Chromium build.
@@ skipping 320 matching lines @@
       "$root_out_dir/natives_blob.bin",
     ]
 
     script = "tools/concatenate-files.py"
 
     args = rebase_path(sources + outputs, root_build_dir)
   }
 }
 
 action("postmortem-metadata") {
-  visibility = [ ":*" ]  # Only targets in this file can depend on this.
+  # Only targets in this file and the top-level visibility target can
+  # depend on this.
+  visibility = [
+    ":*",
+    "//:gn_visibility",
+  ]
 
   script = "tools/gen-postmortem-metadata.py"
 
   sources = [
     "src/objects.h",
     "src/objects-inl.h",
   ]
 
   outputs = [
     "$target_gen_dir/debug-support.cc",
@@ skipping 64 matching lines @@
   configs -= [ "//build/config/compiler:chromium_code" ]
   configs += [ "//build/config/compiler:no_chromium_code" ]
   configs += [
     ":internal_config",
     ":features",
     ":toolchain",
   ]
 }
 
 source_set("v8_snapshot") {
-  visibility = [ ":*" ]  # Only targets in this file can depend on this.
+  # Only targets in this file and the top-level visibility target can
+  # depend on this.
+  visibility = [
+    ":*",
+    "//:gn_visibility",
+  ]
 
   deps = [
     ":js2c",
     ":js2c_experimental",
     ":run_mksnapshot",
     ":v8_base",
   ]
 
   sources = [
     "$target_gen_dir/libraries.cc",
@@ skipping 1169 matching lines @@
       sources += [
         "src/d8-debug.cc",
         "$target_gen_dir/d8-js.cc",
       ]
     }
     if (v8_enable_i18n_support) {
       deps += [ "//third_party/icu" ]
     }
   }
 }