Change record status: 
Project: 
Introduced in branch: 
8.6.x
Description: 

\Drupal\Core\Cache\MemoryCache\MemoryCacheInterface and \Drupal\Core\Cache\MemoryCache\MemoryCache have been added to allow classes that would previously maintain state on a protected property (as a static cache to avoid persistent cache or database lookups) to inject a service to hold that state instead.

The entity.memory_cache has been added, and is now used by all entity storage extending from \Drupal\Core\Entity\EntityStorageBase.

Custom entity storage classes that override __construct() and createInstance() should update to inject the entity.memory_cache service.

Updates Done (doc team, etc.)
Online documentation: 
Not done
Theming guide: 
Not done
Module developer documentation: 
Not done
Examples project: 
Not done
Coder Review: 
Not done
Coder Upgrade: 
Not done
Other: 
Other updates done