TimelineFlameChart: REGRESSION. one line fix after r168084.

BUG=
TBR=apavlov

Review URL: https://codereview.chromium.org/184513002

git-svn-id: svn://svn.chromium.org/blink/trunk@168122 bbb929c8-8fbe-4397-9dbb-9b2b20218538