message: Add a visibility exception for convert_to_constants.
diff: @@ -1586,6 +1586,7 @@ py_library(
  "framework/convert_to_constants.py",
  ],
  srcs_version = "PY2AND3",
  + visibility = visibility + ["//waymo/ml:__subpackages__"],
  deps = [
  ":dtypes",
  ":framework_ops",
  