Use APPLICATION_M3U8 as the mimeType for media playlists.

Given we need to do this in HlsPlaylistParser in the normal
case (i.e. not MEDIA_TAG), we may as well just be consistent
and do it everywhere.

Issue: #151
-------------
Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=111941335

library/src/main/java/com/google/android/exoplayer/hls/HlsChunkSource.java

@@ -212,7 +212,6 @@ public class HlsChunkSource implements HlsTrackSelector.Output {
     if (playlist.type == HlsPlaylist.TYPE_MASTER) {
     if (playlist.type == HlsPlaylist.TYPE_MASTER) {
       masterPlaylist = (HlsMasterPlaylist) playlist;
       masterPlaylist = (HlsMasterPlaylist) playlist;
     } else {
     } else {
-      // TODO: Infer the mime type from a chunk file extension.
       Format format = new Format("0", MimeTypes.APPLICATION_M3U8, -1, -1, -1, -1, -1, -1, null,
       Format format = new Format("0", MimeTypes.APPLICATION_M3U8, -1, -1, -1, -1, -1, -1, null,
           null);
           null);
       List<Variant> variants = new ArrayList<>();
       List<Variant> variants = new ArrayList<>();

library/src/main/java/com/google/android/exoplayer/hls/HlsPlaylistParser.java

@@ -158,8 +158,8 @@ public final class HlsPlaylistParser implements UriLoadable.Parser<HlsPlaylist>
           String subtitleName = HlsParserUtil.parseStringAttr(line, NAME_ATTR_REGEX, NAME_ATTR);
           String subtitleName = HlsParserUtil.parseStringAttr(line, NAME_ATTR_REGEX, NAME_ATTR);
           String uri = HlsParserUtil.parseStringAttr(line, URI_ATTR_REGEX, URI_ATTR);
           String uri = HlsParserUtil.parseStringAttr(line, URI_ATTR_REGEX, URI_ATTR);
           String language = HlsParserUtil.parseOptionalStringAttr(line, LANGUAGE_ATTR_REGEX);
           String language = HlsParserUtil.parseOptionalStringAttr(line, LANGUAGE_ATTR_REGEX);
-          Format format = new Format(subtitleName, MimeTypes.TEXT_VTT, -1, -1, -1, -1, -1, -1,
-              language, codecs);
+          Format format = new Format(subtitleName, MimeTypes.APPLICATION_M3U8, -1, -1, -1, -1, -1,
+              -1, language, codecs);
           subtitles.add(new Variant(uri, format));
           subtitles.add(new Variant(uri, format));
         } else {
         } else {
           // TODO: Support other types of media tag.
           // TODO: Support other types of media tag.