Fix some gn_visibility TODOs.

BUILD.gn

Index: BUILD.gn
diff --git a/BUILD.gn b/BUILD.gn
index 6bde7c0e2bdeaf735027cf86f4823d0ceab66c1c..c56eeafed8044150d7fdf20bf3da2f760ee0b1c9 100644
--- a/BUILD.gn
+++ b/BUILD.gn
@@ -471,9 +471,6 @@ group("both_gn_and_gyp") {
       "//ui/snapshot:snapshot_unittests",
       "//ui/views/examples:views_examples_with_content_exe",
 
-      # "//v8:v8_snapshot",  # TODO(GYP): visibility?
-      # "//v8:postmortem-metadata",  # TODO(GYP): visibility?
-
       "//third_party/codesighs:nm2tsv",
       "//third_party/sqlite:sqlite_shell",
     ]
@@ -742,8 +739,8 @@ group("gn_visibility") {
 
     "//ui/resources:repack_ui_test_mac_locale_pack",
 
-    # "//v8:v8_snapshot",  # TODO(GYP): visibility?
-    # "//v8:postmortem-metadata",  # TODO(GYP): visibility?
+    "//v8:v8_snapshot",
+    "//v8:postmortem-metadata",
   ]
 }