DevTools: highlight stacktrace entries in console error messages

This patch highlights stacktrace entries in console error messages 
with the help of :hover pseudo-class.

BUG=248722

Review URL: https://codereview.chromium.org/110923003

git-svn-id: svn://svn.chromium.org/blink/trunk@163689 bbb929c8-8fbe-4397-9dbb-9b2b20218538