function buildDrmInfo(keySystem, keyIds = [], initData = [],
      encryptionScheme = 'cenc') {
    return jasmine.objectContaining({
      keySystem,
      encryptionScheme,
      keyIds: new Set(keyIds),
      initData,
    });
  }
Build an expected DrmInfo based on a key system and optional key IDs and
init data.

@param {string} keySystem
@param {!Array<string>=} keyIds
@param {!Array<shaka.extern.InitDataOverride>=} initData
@param {string=} encryptionScheme
@return {Object} A DrmInfo-like object.