The old vtt sample data has the header as "WEBVTT FILE" which does not reflect what the spec says it should be. This changes it to "WEBVTT" as described in the WebVTT spec. Change-Id: Ib54396a8b937501a835dafe966bf05b95b0b22c4
Change-Id: Ic69169c31d0a54de4895d49ff8b4a758039733a7