TextTrackCue Extension for WebVTT Regions
https://bugs.webkit.org/show_bug.cgi?id=109821

Reviewed by Eric Carlson.

Source/WebCore:

The TextTrackCue gets a new attribute and setting, regionId, which specifies
to which region the cue belongs to. The attribute is guarded by WEBVTT_REGIONS
and is by default disabled in ports.

Test: media/track/regions-webvtt/text-track-cue-region-attribute.html

* html/track/TextTrackCue.cpp:
(WebCore::TextTrackCue::TextTrackCue): Added member variable for the regionId attribute.
(WebCore):
(WebCore::TextTrackCue::setRegionId): Setter for the regionId attribute.
(WebCore::TextTrackCue::settingName): Added RegionId setting name.
(WebCore::TextTrackCue::setCueSettings): Parsed the "region:" cue setting.
* html/track/TextTrackCue.h:
(TextTrackCue):
(WebCore::TextTrackCue::regionId): Getter for the regionId attribute.
* html/track/TextTrackCue.idl: Updated to match the WebVTT Regions Extension.

LayoutTests:

* media/track/captions-webvtt/header-regions.vtt: Updated to include cues with
settings for which the "region:" setting should be ignored (for backwards compatibility
regarding WebVTT rendering rules).
* media/track/regions-webvtt/text-track-cue-region-attribute-expected.txt: Added.
* media/track/regions-webvtt/text-track-cue-region-attribute.html: Added.


git-svn-id: http://svn.webkit.org/repository/webkit/trunk@147355 268f45cc-cd09-0410-ab3c-d52691b4dbfc