TimelinePanel: fix for strange formatTime code.

TimelineView calculator expected time value that was relative to calculator.minimumBoundary();
It was strange and I fixed that. So now it expects value that is relative to calculator.zeroTime()
i.e. model.minimumRecordTime();

BUG=316167
R=pfeldman@chromium.org

Review URL: https://codereview.chromium.org/177173004

git-svn-id: svn://svn.chromium.org/blink/trunk@167688 bbb929c8-8fbe-4397-9dbb-9b2b20218538