Updated size parameter to match SerializeToArray's function prototype.

This fixes 'implicit conversion loses integer precision' errors on LP64.

PiperOrigin-RevId: 263465379
diff --git a/tensorflow/core/platform/protobuf.h b/tensorflow/core/platform/protobuf.h
index ed23866..d7c4105 100644
--- a/tensorflow/core/platform/protobuf.h
+++ b/tensorflow/core/platform/protobuf.h
@@ -84,7 +84,7 @@
 #ifdef USE_TSTRING
   size_t size = proto.ByteSizeLong();
   output->resize_uninitialized(size);
-  return proto.SerializeToArray(output->data(), size);
+  return proto.SerializeToArray(output->data(), static_cast<int>(size));
 #else   // USE_TSTRING
   return proto.SerializeToString(output);
 #endif  // USE_TSTRING