implement crop operator of TensorflowEmitter. Keras -> Tensorflow nasnet test passed.

mmdnn/conversion/tensorflow/tensorflow_emitter.py

@@ -403,6 +403,21 @@ def KitModel(weight_file = None):
             padding,
             IR_node.name))
 
+    def emit_Crop(self, IR_node):
+        border = IR_node.get_attr('border')
+        assert len(border) == 4
+
+        output_shape = IR_node.get_attr('_output_shapes')[0]
+        output_shape = shape_to_list(output_shape)
+
+        self.add_body(1, "{:<15} = tf.image.crop_to_bounding_box({}, offset_height={}, offset_width={}, target_height={}, target_width={})".format(
+            IR_node.variable_name,
+            self.parent_variable_name(IR_node),
+            border[0],
+            border[2],
+            output_shape[1],
+            output_shape[2]))
+
 
     def _layer_Conv(self):
         self.add_body(0, """

tests/test_conversion_imagenet.py

@@ -200,7 +200,7 @@ class TestModels(CorrectnessTest):
             'densenet'     : [CntkEmit, TensorflowEmit, KerasEmit],
             'xception'     : [TensorflowEmit, KerasEmit],
             'mobilenet'    : [TensorflowEmit, KerasEmit],
-            'nasnet'       : [KerasEmit],
+            'nasnet'       : [TensorflowEmit, KerasEmit],
         }
     }