Correctly calculate highlighted quad for tracing based timeline events

highlightQuad method is added to TimelineMode.Rectord. The method encapsulates logic specific to timeline events and trace events.

BUG=361045
R=caseq@chromium.org

Review URL: https://codereview.chromium.org/326063004

git-svn-id: svn://svn.chromium.org/blink/trunk@175892 bbb929c8-8fbe-4397-9dbb-9b2b20218538