Use the CSS writing-mode rather than the one from VTTCue
Use the CSS writing-mode rather than the one from VTTCue

The DOM element created for a cue box has the writing-mode property
applied. This means that the computed style will trivially map to the
VTTCue value. Also use the logical* (setLogical*) methods from RenderBox
to cut down a bit on the manual handling of the writing mode boilerplate.
This makes RenderVTTCue (SnapToLinesLayouter) look more in line with other
layout code wrt writing-mode.
This eliminates the m_cueWritingDirection state from SnapToLinesLayouter.

BUG=301580

Review URL: https://codereview.chromium.org/882343003

git-svn-id: bf5cd6ccde378db821296732a091cfbcf5285fbd@189193 bbb929c8-8fbe-4397-9dbb-9b2b20218538

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