static setMediaKeySystemAccess(videoCodec, audioCodec, keySystem, mksa) {
    const DrmUtils = shaka.drm.DrmUtils;
    const key = DrmUtils.generateKeySystemCacheKey_(
        videoCodec, audioCodec, keySystem);
    DrmUtils.memoizedMediaKeySystemAccessRequests_.set(key, mksa);
  }
Store MediaKeySystemAccess object associated with specified attributes.

@param {string} videoCodec
@param {string} audioCodec
@param {string} keySystem
@param {!MediaKeySystemAccess} mksa