Move VTT functionality from TextTrackCue.* to VTTCue.*

BUG=270340

Review URL: https://codereview.chromium.org/77853002

git-svn-id: svn://svn.chromium.org/blink/trunk@162550 bbb929c8-8fbe-4397-9dbb-9b2b20218538
If there is two kind of text-decoration, one decoration use outermost color.

Masked currDecs not to propagete the color of the type already
propagated.

Changed currDecs to int to be able to use bitwise operations.
getTextDecorationColors() has already dependend on that ETextDecoration
is flag. This fix doesn't add assumption.

Flag type should use unsigned. Changed the flag type from int to unsigned.

BUG=321910

Review URL: https://codereview.chromium.org/80313002

git-svn-id: svn://svn.chromium.org/blink/trunk@162551 bbb929c8-8fbe-4397-9dbb-9b2b20218538