message: Define getDialectNamespace method for the TensorFlow dialect
  Required to register TensorFlow ops in ConversionTarget for DialectConversion
diff: @@ -38,6 +38,8 @@ class TensorFlowDialect : public Dialect {
  public:
  TensorFlowDialect(MLIRContext *context);
  + static StringRef getDialectNamespace() { return "tf"; }
  +
  // Gradient attribute ("tf.gradient") in the list of NamedAttibutes in a
  // function references to its gradient function. This attribute in TensorFlow
  // Dialect is used to model TF GradientDef. GetGradientAttrName() returns the
  