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.
The original HttpKernel class can be deleted, as it's request-stashing will be moved to the Kernel class. FrameworkBundle's list of compiled classes must also be modified to respect this change.
