The calling context is the second top-most non-debugger context on the
stack, but that's not necessarily the actually calling context, e.g.,
when a tail-call was used.

BUG=chromium:541703
R=verwaest@chromium.org
LOG=y

Review URL: https://codereview.chromium.org/1431473003

Cr-Commit-Position: refs/heads/master@{#31719}