11 files declare their use of ContactInterface in CRM Core 8.2

Activity.php in modules/crm_core_activity/src/Entity/Activity.php

ActivityInterface.php in modules/crm_core_activity/src/ActivityInterface.php

Contains \Drupal\crm_core_activity\ActivityInterface.

DateFieldHandler.php in modules/crm_core_match/src/Plugin/crm_core_match/field/DateFieldHandler.php

DefaultMatchingEngine.php in modules/crm_core_match/src/Plugin/crm_core_match/engine/DefaultMatchingEngine.php

FieldHandlerBase.php in modules/crm_core_match/src/Plugin/crm_core_match/field/FieldHandlerBase.php

FieldHandlerInterface.php in modules/crm_core_match/src/Plugin/crm_core_match/field/FieldHandlerInterface.php

MatchEngineInterface.php in modules/crm_core_match/src/Plugin/crm_core_match/engine/MatchEngineInterface.php

Contains \Drupal\crm_core_match\Plugin\crm_core_match\engine\MatchEngineInterface.

Matcher.php in modules/crm_core_match/src/Entity/Matcher.php

Contains \Drupal\crm_core_match\Entity\Matcher.

MatcherConfigInterface.php in modules/crm_core_match/src/Matcher/MatcherConfigInterface.php

Contains \Drupal\crm_core_match\Matcher\MatcherConfigInterface.

NameFieldHandler.php in modules/crm_core_match/src/Plugin/crm_core_match/field/NameFieldHandler.php

Organization.php in modules/crm_core_contact/src/Entity/Organization.php