fix visible part of the newly recording FlameChart in 1 second range

BUG=312167
R=pfeldman@chromium.org

Review URL: https://codereview.chromium.org/163503002

git-svn-id: svn://svn.chromium.org/blink/trunk@167569 bbb929c8-8fbe-4397-9dbb-9b2b20218538