TextTrackList not sorted correctly

TextTrackList not sorted correctly
https://bugs.webkit.org/show_bug.cgi?id=72545

Reviewed by Darin Adler.

Source/WebCore:

Test: media/track/track-texttracks.html

* WebCore.xcodeproj/project.pbxproj: Add TextTrack.h to WebCore private headers because
    it is included by HTMLMediaElement.h.
* html/LoadableTextTrack.cpp:
(WebCore::LoadableTextTrack::LoadableTextTrack): Pass track type to base class constructor.
(WebCore::LoadableTextTrack::trackElementIndex): New, return the <track> element's tree order
    for sorting.
* html/LoadableTextTrack.h:

* html/TextTrack.cpp:
(WebCore::TextTrack::TextTrack): Set track type.
* html/TextTrack.h:
(WebCore::TextTrack::create): Ditto.
(WebCore::TextTrack::trackType): Ditto.

* html/track/TextTrackList.cpp:
(TextTrackList::length): Update to deal with two TextTrack vectors.
(TextTrackList::item): Ditto.
(TextTrackList::append): Ditto.
(TextTrackList::remove): Ditto
* html/track/TextTrackList.h: Store the two types of TextTracks in separate Vectors to make
    it simpler to keep them in the correct order.

LayoutTests:

* media/track/track-texttracks-expected.txt: Added.
* media/track/track-texttracks.html: Added.

git-svn-id: http://svn.webkit.org/repository/webkit/trunk@100616 268f45cc-cd09-0410-ab3c-d52691b4dbfc