Move Web Animations specific excpectation and update bug reference

No functional change.

BUG=258896,277005
TBR=jianli

Review URL: https://codereview.chromium.org/22890008

git-svn-id: svn://svn.chromium.org/blink/trunk@156521 bbb929c8-8fbe-4397-9dbb-9b2b20218538