Fix typo in TimelineView highlighter

This was introduced in r176205.

BUG=None
TBR=caseq

Review URL: https://codereview.chromium.org/339873002

git-svn-id: svn://svn.chromium.org/blink/trunk@176297 bbb929c8-8fbe-4397-9dbb-9b2b20218538