Create bindings so that MediaStreamTrackPrivate can be cast to either VideoTrackPrivate or AudioTrackPrivate

[Matthew Daiter]

Need to do this in order to make sure that the MediaStreamTrackPrivate can be interpreted by the MediaStream Engine

[Radar WebKit Bug Importer]

<rdar://problem/21821125>

[Matthew Daiter]

Created attachment 256842 [details]
Patch

[Matthew Daiter]

Created attachment 256843 [details]
Patch

[Matthew Daiter]

Created attachment 256847 [details]
Patch

[Eric Carlson]

Comment on attachment 256847 [details]
Patch

View in context: https://bugs.webkit.org/attachment.cgi?id=256847&action=review

> Source/WebCore/ChangeLog:8
> +        Reviewed by NOBODY (OOPS!).
> +

Please add tests.

> Source/WebCore/Modules/mediastream/MediaStreamTrack.cpp:197
> +    return true;

Only "main" should return true.

> Source/WebCore/Modules/mediastream/MediaStreamTrack.cpp:203
> +    return emptyAtom;

The spec says: 

    AudioTrack.kind and VideoTrack.kind be "main"

> Source/WebCore/Modules/mediastream/MediaStreamTrack.cpp:241
> +    setLanguage(language);

The spec says:

    AudioTrack.language and VideoTrack.language be the empty string

> Source/WebCore/Modules/mediastream/MediaStreamTrack.cpp:247
> +    // Still haven't dealt with enabling MediaStreamTracks and whether to treat as separate objects inside of HTMLMediaElement yet.
> +    notImplemented();

The spec says:

    If a MediaStreamTrack is removed from a MediaStream, played by a media element, the corresponding AudioTrack or VideoTrack must be removed as well.

> Source/WebCore/platform/mediastream/MediaStreamTrackPrivate.h:91
> +

Nit: you don't need this extra blank line

[Jon Lee]

This was done elsewhere.