Eliminate url() method on TimelineModel.Record

All its usages have been inlined.

BUG=361045
R=alph@chromium.org

Review URL: https://codereview.chromium.org/305133004

git-svn-id: svn://svn.chromium.org/blink/trunk@175263 bbb929c8-8fbe-4397-9dbb-9b2b20218538