static filterTextStreams_(manifest) {
    // Filter text streams.
    manifest.textStreams = manifest.textStreams.filter((stream) => {
      const fullMimeType = shaka.util.MimeUtils.getFullType(
          stream.mimeType, stream.codecs);
      const keep = shaka.text.TextEngine.isTypeSupported(fullMimeType);

      if (!keep) {
        shaka.log.debug('Dropping text stream. Is not supported by the ' +
                        'platform.', stream);
      }

      return keep;
    });
  }
Alters the given Manifest to filter out any unsupported text streams.

@param {shaka.extern.Manifest} manifest
@private