static isCompatible_(a, b) {
    const ArrayUtils = shaka.util.ArrayUtils;

    // TODO: Add a way to change the license server in DrmEngine to avoid
    // resetting EME for different license servers.
    const comp = (x, y) =>
      x.robustness == y.robustness && x.contentType == y.contentType;
    return a.keySystem == b.keySystem && a.licenseUri == b.licenseUri &&
        ArrayUtils.hasSameElements(
            a.audioCapabilities, b.audioCapabilities, comp) &&
        ArrayUtils.hasSameElements(
            a.videoCapabilities, b.videoCapabilities, comp);
  }
Returns whether the given session infos are compatible with each other.
@param {shaka.extern.EmeSessionDB} a
@param {shaka.extern.EmeSessionDB} b
@return {boolean}
@private