Inline usages of TimelineRecordImpl.highlightQuad

The field is used in a single place, no need to store it on the record.

BUG=
R=caseq@chromium.org, loislo@chromium.org

Review URL: https://codereview.chromium.org/286903009

git-svn-id: svn://svn.chromium.org/blink/trunk@174451 bbb929c8-8fbe-4397-9dbb-9b2b20218538