Add EagerTensor.AsContatnt().

src/TensorFlowNET.Core/Eager/EagerTensor.Creation.cs

@@ -66,15 +66,30 @@ namespace Tensorflow.Eager
             Tensor placeholder = null;
             tf_with(ops.control_dependencies(null), delegate
             {
-                placeholder = tf.placeholder(dtype, shape: shape, name: name ?? this.name);
+                placeholder = tf.placeholder(dtype, name: name);
             });
-            // custom_gradient.copy_handle_data(value, placeholder)
+            copy_handle_data(placeholder);
             return placeholder;
         }
 
-        void copy_handle_data()
+        public Tensor AsContatnt(string name = null)
         {
+            Tensor constant = null;
+            tf_with(ops.control_dependencies(null), delegate
+            {
+                constant = tf.constant(numpy(), name: name);
+            });
+            return constant;
+        }
 
+        void copy_handle_data(Tensor target_t)
+        {
+            if(target_t.dtype == TF_DataType.TF_RESOURCE ||
+                target_t.dtype == TF_DataType.TF_VARIANT)
+            {
+                // need to export
+                // c_api.TF_GraphSetOutputHandleShapesAndTypes(target_t.graph, target_t._as_tf_output(), 0, new IntPtr[0], new int[0], new DataType[0], tf.Status.Handle);
+            }
         }
 
         public override IntPtr ToPointer()