Fix race conditions in animations/transitions tests.

These tests were all kicking off an animation/transition before the
first recalc was guaranteed to happen. Mostly the tests happen to work,
but they break when we turn on lazy attaching from the parser.

Review URL: https://chromiumcodereview.appspot.com/23461011

git-svn-id: svn://svn.chromium.org/blink/trunk@156815 bbb929c8-8fbe-4397-9dbb-9b2b20218538