When DevTools calls to JavaScript, it often ignores exceptions and just
fails since no value was returned.
The new --print-all-exceptions flag makes it easy to spot the location
and the reason for the thrown exception.

R=titzer@chromium.org

Review-Url: https://codereview.chromium.org/2417743004
Cr-Commit-Position: refs/heads/master@{#40340}