This method is a slight misnomer. What we actually want to know is
whether the function was defined in a user-provided script.

Also remove redundant Script::hide_source flag.

R=bmeurer@chromium.org, ulan@chromium.org

Review-Url: https://codereview.chromium.org/2505853003
Cr-Commit-Position: refs/heads/master@{#41036}