DevTools: unflake inspector-protocol/timeline/timeline-start-bufferEvents.html

BUG=317556
TBR=caseq

Review URL: https://codereview.chromium.org/63553004

git-svn-id: svn://svn.chromium.org/blink/trunk@161734 bbb929c8-8fbe-4397-9dbb-9b2b20218538