Use TimelineModel.Record methods instead of raw protocol data

In timeline tests TimelineModel.Record interface is used instead of raw protocol data to dump collected timeline events.

BUG=398785

Review URL: https://codereview.chromium.org/486673002

git-svn-id: svn://svn.chromium.org/blink/trunk@180537 bbb929c8-8fbe-4397-9dbb-9b2b20218538