The parser reads one character beyond EOF to have an additional source
position that the rewriter can use to insert the implicit return
statement at the end of a script. If we break at that return statement,
we need to be able to translate the source position to line and
column number.

R=jkummerow@chromium.org

Review URL: https://codereview.chromium.org/1521953003

Cr-Commit-Position: refs/heads/master@{#32825}