message: In op level cost estimator, use PredictMetadata() for ShapeN operation.
diff: @@ -54,6 +54,7 @@ constexpr char kVariable[] = "Variable";
  constexpr char kVariableV2[] = "VariableV2";
  constexpr char kRank[] = "Rank";
  constexpr char kShape[] = "Shape";
  +constexpr char kShapeN[] = "ShapeN";
  constexpr char kSize[] = "Size";
  constexpr char kStopGradient[] = "StopGradient";
  constexpr char kPreventGradient[] = "PreventGradient";
  @@ -264,6 +265,7 @@ OpLevelCostEstimator::OpLevelCostEstimator() {
  {kRank, wrap(&OpLevelCostEstimator::PredictMetadata)},
  {kShape, wrap(&OpLevelCostEstimator::PredictMetadata)},
  + {kShapeN, wrap(&OpLevelCostEstimator::PredictMetadata)},
  {kSize, wrap(&OpLevelCostEstimator::PredictMetadata)},
  {kMaxPool, wrap(&OpLevelCostEstimator::PredictMaxPool)},
  {kMaxPoolGrad, wrap(&OpLevelCostEstimator::PredictMaxPoolGrad)},
  