DevTools: add initial support for console.time/timeEnd in tracing based Timeline

console.time/timeEnd will result in instant trace events. The events will be shown as marker events, i.e. as markers on the Timeline overview.

BUG=361045

Review URL: https://codereview.chromium.org/464063008

git-svn-id: svn://svn.chromium.org/blink/trunk@180635 bbb929c8-8fbe-4397-9dbb-9b2b20218538