static ObtainBaseImageLayerStep forForcedDownload(
      BuildContext buildContext,
      ProgressEventDispatcher.Factory progressEventDispatcherFactory,
      Layer layer,
      @Nullable RegistryClient sourceRegistryClient) {
    BlobExistenceChecker noOpChecker = ignored -> StateInTarget.UNKNOWN;
    return new ObtainBaseImageLayerStep(
        buildContext, progressEventDispatcherFactory, layer, sourceRegistryClient, noOpChecker);
  }
Pulls and caches a single base image layer.
jib-core/src/main/java/com/google/cloud/tools/jib/builder/steps/ObtainBaseImageLayerStep.java