Calls to AbstractApplicationContext#setParent delegate the parent
context environment to the child.
This ensures that any property sources added to the parent are available
to the child as well as ensuring that any profiles activated are
activated everywhere.
Child contexts may still choose to replace their environment (through an
ApplicationContextInitializer, for example). In any case, however, in
the root/child web application context relationship established by
ContextLoader + DispatcherServlet, the child is guaranteed to have
already been given the parent environment by the time it is delegated
to any ACIs.
See AbstractApplicationContext#setParent for implementation
See FrameworkServlet#createWebApplicationContext for order in which
setParent then initializeWebApplicationContext are called.
Issue: SPR-8185
c4363673dc