10 files declare their use of NormalizerInterface

ChainEntityResolver.php in drupal/core/modules/serialization/lib/Drupal/serialization/EntityResolver/ChainEntityResolver.php
Contains \Drupal\serialization\EntityResolver\ChainEntityResolver
Dummy.php in drupal/core/vendor/symfony/serializer/Symfony/Component/Serializer/Tests/Fixtures/Dummy.php
EntityResolverInterface.php in drupal/core/modules/serialization/lib/Drupal/serialization/EntityResolver/EntityResolverInterface.php
Contains \Drupal\serialization\EntityResolver\EntityResolverInterface
NormalizableTraversableDummy.php in drupal/core/vendor/symfony/serializer/Symfony/Component/Serializer/Tests/Fixtures/NormalizableTraversableDummy.php
NormalizerBase.php in drupal/core/modules/serialization/lib/Drupal/serialization/Normalizer/NormalizerBase.php
Contains \Drupal\serialization\Normalizer\NormalizerBase.
ScalarDummy.php in drupal/core/vendor/symfony/serializer/Symfony/Component/Serializer/Tests/Fixtures/ScalarDummy.php
SerializationTestNormalizer.php in drupal/core/modules/serialization/tests/serialization_test/lib/Drupal/serialization_test/SerializationTestNormalizer.php
Contains \Drupal\serialization_test\SerializationTestNormalizer.
Serializer.php in drupal/core/vendor/symfony/serializer/Symfony/Component/Serializer/Serializer.php
TestNormalizer.php in drupal/core/vendor/symfony/serializer/Symfony/Component/Serializer/Tests/Normalizer/TestNormalizer.php
UuidResolver.php in drupal/core/modules/serialization/lib/Drupal/serialization/EntityResolver/UuidResolver.php
Contains \Drupal\serialization\EntityResolver\UuidResolver