initDataOverrideEqual = (a, b) => {
      if (a.keyId && a.keyId == b.keyId) {
        // Two initDatas with the same keyId are considered to be the same,
        // unless that "same keyId" is null.
        return true;
      }
      return a.initDataType == b.initDataType &&
         shaka.util.BufferUtils.equal(a.initData, b.initData);
    }
@type {function(shaka.extern.InitDataOverride,
                shaka.extern.InitDataOverride):boolean}