Fix unhandled promise console message to show stack trace of a DOMException.

BUG=393913
R=pfeldman@chromium.org, yurys@chromium.org

Review URL: https://codereview.chromium.org/660543002

git-svn-id: svn://svn.chromium.org/blink/trunk@183985 bbb929c8-8fbe-4397-9dbb-9b2b20218538