DTS Express (which is DTS LBR according to http://www.mp4ra.org/codecs.html) is
not supported for passthrough playback currently. Associate a different MIME
type with it so that we don't try to use DTS passthrough for playing DTS
Express.
The MIME type for DTS Express is just vnd.dts.hd, with a profile parameter
indicating that it's DTS Express rather than one of the other formats.
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Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=117129583
