DevTools: Don't append async call stack to console stack when looking only for a top call frame.

In this common special case we do not need async call stack.

R=yurys

Review URL: https://codereview.chromium.org/428923004

git-svn-id: svn://svn.chromium.org/blink/trunk@179398 bbb929c8-8fbe-4397-9dbb-9b2b20218538