DevTools: do not special-case TimerFire stack

FunctionCall could have additional details that we are discarding.

R=caseq@chromium.org

Review URL: https://codereview.chromium.org/183743009

git-svn-id: svn://svn.chromium.org/blink/trunk@168118 bbb929c8-8fbe-4397-9dbb-9b2b20218538