DevTools: allow whitelist of timeline events to be pushed live although in bufferEvent mode.

R=caseq@chromium.org

Review URL: https://codereview.chromium.org/213003002

git-svn-id: svn://svn.chromium.org/blink/trunk@170186 bbb929c8-8fbe-4397-9dbb-9b2b20218538