[Update]

  Refactor optimization pass through grappler
    tensorflow fixed dependency issues in
      core/grappler/constant_folding
    removed python calls for optimization(layout/constfold), moved optimization
    to convert_graph.cc

  bug:
    dependency issue with //tensorflow/core/grappler/clusters:single_machine

  TODO:
    shape inference through grappler.
    cluster for optimization pass.