Fix BiDi paragraph embedding level resolution for VTTCue

Fix BiDi paragraph embedding level resolution for VTTCue

Iterate over code points rather than (UTF-16) code units.
Make determineTextDirection side-effect free and local to the compilation
unit.
Re-uses the BidiResolver to do the actual work, and removes the
concatenation of the textnodes.

BUG=322051
Committed: https://src.chromium.org/viewvc/blink?view=rev&revision=162920

[eseidel, 2013-11-21 16:12:48]

Sad panda.  Why does TextTrackCue have it's own bidi code?

[fs, 2013-11-21 16:24:33]

On 2013/11/21 16:12:48, eseidel wrote:
> Sad panda.  Why does TextTrackCue have it's own bidi code?

That's a good question that I unfortunately lack the answer too. Prompted by
this though I found determineDirectionality in HTMLElement.cpp, which looks like
it might fit the bill (if moved somewhere else). I'll look into using that
instead. (Looking at BidiResolver::determineParagraphDirectionality though it
seems to suffer from the same issue...)

[eseidel, 2013-11-21 16:30:17]

EditorStyle.cpp also has its own directionalty determining code for which there
is a bug on file:
https://code.google.com/p/chromium/issues/detail?id=296847

[vcarbune.chromium, 2013-11-21 22:02:11]

On 2013/11/21 16:24:33, fs wrote:
> On 2013/11/21 16:12:48, eseidel wrote:
> > Sad panda.  Why does TextTrackCue have it's own bidi code?
> 
> That's a good question that I unfortunately lack the answer too.

Just to add context, here's the WK bug with
the discussion around this code: http://wkb.ug/79749

[fs, 2013-11-22 12:57:54]

New, more panda-happiness friendly, attempt. Does however depend on the likes of
https://codereview.chromium.org/83443002/.

[eseidel, 2013-11-22 18:53:56]

lgtm

Definitely better to share code when possible.  Thanks.

[fs, 2013-11-29 17:26:34]

Rebase needed after code moved from TextTrackCue -> VTTCue.

[commit-bot: I haz the power, 2013-11-29 17:46:19]

CQ is trying da patch. Follow status at
https://chromium-status.appspot.com/cq/fs@opera.com/81133002/120001

[commit-bot: I haz the power, 2013-11-29 18:33:18]

Change committed as 162920