Enable disabled animaition tests.

r176165 disabled three tests, but two are innocent.
overlay-background-color-transitions.html causes oom, and innocent two tests
were victim of oom. So enable them again.

BUG=384857

Review URL: https://codereview.chromium.org/432263003

git-svn-id: svn://svn.chromium.org/blink/trunk@179519 bbb929c8-8fbe-4397-9dbb-9b2b20218538