Bug 284543

There are 7 failing subtests in scroll-animations/scroll-timelines/play-animation.html: FAIL Playing a running animation resets a sticky start time assert_approx_equals: values do not match for "undefined" expected 0 +/- 0.125 but got 10 FAIL Playing a finished animation restarts the animation aligned at the start assert_approx_equals: values do not match for "undefined" expected 0 +/- 0.125 but got 100 FAIL Playing a finished and reversed animation restarts the animation aligned at the end assert_approx_equals: values do not match for "undefined" expected 100 +/- 0.125 but got 0 FAIL Playing a pause-pending but previously finished animation realigns with the scroll position assert_approx_equals: values do not match for "After aborting a pause when finished, the start time should no longer be sticky" expected 0 +/- 0.125 but got -50 FAIL Playing a finished animation clears the start time assert_approx_equals: values do not match for "start time is zero" expected 0 +/- 0.125 but got -100 FAIL Resuming an animation from paused realigns with scroll position. assert_approx_equals: values do not match for "undefined" expected 0 +/- 0.125 but got -50 FAIL A pending playback rate is used when determining timeline range alignment assert_approx_equals: values do not match for "undefined" expected 100 +/- 0.125 but got -100