/usr/share/php/Symfony/Component/Serializer/ is in php-symfony-serializer 2.7.10-0ubuntu2.
This file is owned by root:root, with mode 0o755.
..
/usr/share/php/Symfony/Component/Serializer/Annotation/
/usr/share/php/Symfony/Component/Serializer/Annotation/Groups.php
/usr/share/php/Symfony/Component/Serializer/Encoder/
/usr/share/php/Symfony/Component/Serializer/Encoder/ChainDecoder.php
/usr/share/php/Symfony/Component/Serializer/Encoder/ChainEncoder.php
/usr/share/php/Symfony/Component/Serializer/Encoder/DecoderInterface.php
/usr/share/php/Symfony/Component/Serializer/Encoder/EncoderInterface.php
/usr/share/php/Symfony/Component/Serializer/Encoder/JsonDecode.php
/usr/share/php/Symfony/Component/Serializer/Encoder/JsonEncode.php
/usr/share/php/Symfony/Component/Serializer/Encoder/JsonEncoder.php
/usr/share/php/Symfony/Component/Serializer/Encoder/NormalizationAwareInterface.php
/usr/share/php/Symfony/Component/Serializer/Encoder/SerializerAwareEncoder.php
/usr/share/php/Symfony/Component/Serializer/Encoder/XmlEncoder.php
/usr/share/php/Symfony/Component/Serializer/Exception/
/usr/share/php/Symfony/Component/Serializer/Exception/CircularReferenceException.php
/usr/share/php/Symfony/Component/Serializer/Exception/Exception.php
/usr/share/php/Symfony/Component/Serializer/Exception/ExceptionInterface.php
/usr/share/php/Symfony/Component/Serializer/Exception/InvalidArgumentException.php
/usr/share/php/Symfony/Component/Serializer/Exception/LogicException.php
/usr/share/php/Symfony/Component/Serializer/Exception/MappingException.php
/usr/share/php/Symfony/Component/Serializer/Exception/RuntimeException.php
/usr/share/php/Symfony/Component/Serializer/Exception/UnexpectedValueException.php
/usr/share/php/Symfony/Component/Serializer/Exception/UnsupportedException.php
/usr/share/php/Symfony/Component/Serializer/Mapping/
/usr/share/php/Symfony/Component/Serializer/Mapping/AttributeMetadata.php
/usr/share/php/Symfony/Component/Serializer/Mapping/AttributeMetadataInterface.php
/usr/share/php/Symfony/Component/Serializer/Mapping/ClassMetadata.php
/usr/share/php/Symfony/Component/Serializer/Mapping/ClassMetadataInterface.php
/usr/share/php/Symfony/Component/Serializer/Mapping/Factory/
/usr/share/php/Symfony/Component/Serializer/Mapping/Factory/ClassMetadataFactory.php
/usr/share/php/Symfony/Component/Serializer/Mapping/Factory/ClassMetadataFactoryInterface.php
/usr/share/php/Symfony/Component/Serializer/Mapping/Loader/
/usr/share/php/Symfony/Component/Serializer/Mapping/Loader/AnnotationLoader.php
/usr/share/php/Symfony/Component/Serializer/Mapping/Loader/FileLoader.php
/usr/share/php/Symfony/Component/Serializer/Mapping/Loader/LoaderChain.php
/usr/share/php/Symfony/Component/Serializer/Mapping/Loader/LoaderInterface.php
/usr/share/php/Symfony/Component/Serializer/Mapping/Loader/XmlFileLoader.php
/usr/share/php/Symfony/Component/Serializer/Mapping/Loader/YamlFileLoader.php
/usr/share/php/Symfony/Component/Serializer/Mapping/Loader/schema/
/usr/share/php/Symfony/Component/Serializer/Mapping/Loader/schema/dic/
/usr/share/php/Symfony/Component/Serializer/Mapping/Loader/schema/dic/serializer-mapping/
/usr/share/php/Symfony/Component/Serializer/Mapping/Loader/schema/dic/serializer-mapping/serializer-mapping-1.0.xsd
/usr/share/php/Symfony/Component/Serializer/NameConverter/
/usr/share/php/Symfony/Component/Serializer/NameConverter/CamelCaseToSnakeCaseNameConverter.php
/usr/share/php/Symfony/Component/Serializer/NameConverter/NameConverterInterface.php
/usr/share/php/Symfony/Component/Serializer/Normalizer/
/usr/share/php/Symfony/Component/Serializer/Normalizer/AbstractNormalizer.php
/usr/share/php/Symfony/Component/Serializer/Normalizer/CustomNormalizer.php
/usr/share/php/Symfony/Component/Serializer/Normalizer/DenormalizableInterface.php
/usr/share/php/Symfony/Component/Serializer/Normalizer/DenormalizerInterface.php
/usr/share/php/Symfony/Component/Serializer/Normalizer/GetSetMethodNormalizer.php
/usr/share/php/Symfony/Component/Serializer/Normalizer/NormalizableInterface.php
/usr/share/php/Symfony/Component/Serializer/Normalizer/NormalizerInterface.php
/usr/share/php/Symfony/Component/Serializer/Normalizer/ObjectNormalizer.php
/usr/share/php/Symfony/Component/Serializer/Normalizer/PropertyNormalizer.php
/usr/share/php/Symfony/Component/Serializer/Normalizer/SerializerAwareNormalizer.php
/usr/share/php/Symfony/Component/Serializer/Serializer.php
/usr/share/php/Symfony/Component/Serializer/SerializerAwareInterface.php
/usr/share/php/Symfony/Component/Serializer/SerializerInterface.php
/usr/share/php/Symfony/Component/Serializer/autoload.php