Possible issue with EntityCacheControllerHelper::resetEntityCache()

Problem/Motivation

It looks like the current cache clearing implementation in EntityCacheControllerHelper::resetEntityCache() is wrong. This could lead to unexpected behaviour if an explicit cache clear is requested.

The current code looks like this:

    // Reset the persistent cache.
    if (isset($ids)) {
      cache_clear_all($ids, 'cache_entity_' . $controller->entityType);
    }

If I understand that right the cache_clear_all is called only if $ids is set (and is not NULL).
According to DrupalEntityControllerInterface::resetCache() $ids can be NULL and in such case the whole cache has to be cleared.
This means EntityCacheControllerHelper::resetEntityCache() misses a handling for the case $ids is NULL.
Further cache_clear_all() doesn't seem to support an array as $cid - this means passing the $ids as parameter for $cid won't lead to the expected behaviour.

Proposed resolution

• Add iteration over $ids to call cache_clear_all() - similar approach as this, never comitted one, here: #1050562: Does not support $reset argument
• Add handling for the case $ids is NULL. I'm not sure yet what to use:
  • cache_clear_all(NULL, 'cache_entity_' . $controller->entityType); - deletes only expired items.
  • cache_clear_all('*', 'cache_entity_' . $controller->entityType, TRUE); - deletes all items and seems to work better, but that can be caused by the fact I used memcache to test this.

Remaining tasks

Review patch.
Decide which cache_clear_all() call should be used in the "$ids is NULL" case.

User interface changes

none

API changes

none