Add Keras metadata proto.

The metadata of each Keras model/layer will be moved from the SavedModel to a separate keras.metadata file.

PiperOrigin-RevId: 337394096
Change-Id: Iccba44c8478e038fc9de036313c2e7e88fd5605d

tensorflow/python/keras/protobuf/BUILD

@@ -14,3 +14,10 @@ tf_proto_library(
     srcs = ["projector_config.proto"],
     cc_api_version = 2,
 )
+
+tf_proto_library(
+    name = "saved_metadata_proto",
+    srcs = ["saved_metadata.proto"],
+    cc_api_version = 2,
+    protodeps = ["//tensorflow/core:protos_all"],
+)

tensorflow/python/keras/protobuf/saved_metadata.proto

@@ -0,0 +1,33 @@
+// Protobuf containing the metadata for each Keras object saved in a SavedModel.
+
+syntax = "proto3";
+
+package third_party.tensorflow.python.keras.protobuf;
+
+import "tensorflow/core/framework/versions.proto";
+
+message SavedMetadata {
+  // Nodes represent trackable objects in the SavedModel. The data for every
+  // Keras object is stored.
+  repeated SavedObject nodes = 1;
+}
+
+// Metadata of an individual Keras object.
+message SavedObject {
+  // Version defined by the code serializing this Keras object.
+  .tensorflow.VersionDef version = 1;
+  // Index of the node in the SavedModel SavedObjectGraph.
+  int32 node_id = 2;
+  // String path from root (e.g. "root.child_layer")
+  string node_path = 3;
+
+  // Identifier to determine loading function.
+  // Currently supported identifiers:
+  //   _tf_keras_layer, _tf_keras_input_layer, _tf_keras_rnn_layer,
+  //   _tf_keras_metric, _tf_keras_network, _tf_keras_model,
+  //   _tf_keras_sequential
+  string identifier = 4;
+  // Metadata containing a JSON-serialized object with the non-TensorFlow
+  // attributes for this Keras object.
+  string metadata = 5;
+}