Issue #1774332 by c960657: Better handling of invalid/expired cache entries.

core/includes/cache.inc

core/includes/common.inc

core/includes/entity.inc

core/includes/menu.inc

core/includes/schema.inc

core/includes/update.inc

core/lib/Drupal/Core/Cache/BackendChain.php

core/lib/Drupal/Core/Cache/CacheBackendInterface.php

core/lib/Drupal/Core/Cache/DatabaseBackend.php

core/lib/Drupal/Core/Cache/InstallBackend.php

core/lib/Drupal/Core/Cache/MemoryBackend.php

core/lib/Drupal/Core/Cache/NullBackend.php

core/modules/aggregator/aggregator.parser.inc

core/modules/block/block.admin.inc

core/modules/block/lib/Drupal/block/Tests/BlockCacheTest.php

core/modules/comment/comment.admin.inc

core/modules/comment/comment.module

...ules/comment/lib/Drupal/comment/CommentFormController.php

...les/comment/lib/Drupal/comment/Tests/CommentBlockTest.php

core/modules/field/field.info.inc