The only missing part is ContainerAwareEventManager::addEventSubscriberService(),
because I'm not sure how to find out the class name of a service in the DIC.
Also, inline documentation of this code needs to be finished once it is accepted.
Rules are :
- If one of the ESI has validation cache strategy, the whole page will be
forced to validate.
- In none of the ESI has validation, the response will feature a Cache-Control
directive with s-maxage value equals to the smallest TTL of ESIs.