[e2e] fix tf1 hashtable test (#7904)

* initialize graph_def library field if it is not set

* Update tf_saved_model_conversion_v2.py

tfjs-converter/python/tensorflowjs/converters/tf_saved_model_conversion_v2.py

@@ -27,6 +27,7 @@
 # Required to load saved models that use TFDF.
 import tensorflow_decision_forests
 import tensorflow as tf
+from tensorflow.core.framework import function_pb2
 from tensorflow.core.framework import graph_pb2
 from tensorflow.core.framework import node_def_pb2
 from tensorflow.core.protobuf import config_pb2
@@ -432,6 +433,8 @@ def _freeze_saved_model_v1(saved_model_dir, saved_model_tags,
       meta_graph = loader.load(sess, saved_model_tags, saved_model_dir)
 
       meta_graph_def = g.as_graph_def()
+      if not meta_graph_def.HasField('library'):
+        meta_graph_def.library.CopyFrom(function_pb2.FunctionDefLibrary())
 
       frozen_graph_def = tf.compat.v1.graph_util.convert_variables_to_constants(
           sess, meta_graph_def, output_node_names)