Minor adjustment to WebVTT tests

Do a trivial adjustment to the tc029-timings-whitespace test to make
it robust against the spec. change that disallows --> in cue text.

Fix test opera/interfaces/TextTrackCue/vertical.html to it possible
to pass it (the expected result is still FAIL), by adding a linebreak.

BUG=305317

Review URL: https://codereview.chromium.org/59153008

git-svn-id: svn://svn.chromium.org/blink/trunk@161931 bbb929c8-8fbe-4397-9dbb-9b2b20218538