DevTools: Add timestamp support in the console

Add a setting which when enabled will append a time stamp to each
message in the console.

BUG=131714

Review URL: https://codereview.chromium.org/185713007

git-svn-id: svn://svn.chromium.org/blink/trunk@170055 bbb929c8-8fbe-4397-9dbb-9b2b20218538