Split VTTCue from TextTrackCue

VTTCue has been split from TextTrackCue in the specs:
http://whatwg.org/html#texttrackcue
http://dev.w3.org/html5/webvtt/#vttcue-interface

The TextTrackCue constructor is left for legacy compat until it is
deemed safe to remove. To verify that it actually works, the tests still
use the TextTrackCue constructor, but will be updated to use VTTCue in a
later commit.

Internal refactoring has been kept to a minimum, future commits should
move more code from TextTrackCue to VTTCue.

Thanks to Glenn Adams for starting this work and providing feedback!

BUG=270340

Review URL: https://codereview.chromium.org/63173020

git-svn-id: svn://svn.chromium.org/blink/trunk@162015 bbb929c8-8fbe-4397-9dbb-9b2b20218538
Simplify settings integration to NamedBitSetFilter.

BUG=
R=vsevik@chromium.org

Review URL: https://codereview.chromium.org/63243005

git-svn-id: svn://svn.chromium.org/blink/trunk@162016 bbb929c8-8fbe-4397-9dbb-9b2b20218538