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

Existing async events with category blink.timeline are reused for DevTools needs. The events will be shown as marker events, i.e. as markers on the Timeline overview.

BUG=361045
R=caseq@chromium.org

Review URL: https://codereview.chromium.org/497493002

git-svn-id: svn://svn.chromium.org/blink/trunk@180711 bbb929c8-8fbe-4397-9dbb-9b2b20218538