Unfortunately, we cannot just simply unset the wl_global's user data.
The compositor still needs to process client requests after the global
has been removed, for example bind requests or the requests that create
new resources.
CCBUG: 435258
Getting the object associated with the particular wl_resource is not
difficult, but it involves a pretty reasonable amount of boilerplate
code.
This change, introduces a helper function with an intend to reduce the
amount of boilerplate code.
It can be used as resource_cast<const ObjectPrivate *>(resource) or
just simply resource_cast<ObjectPrivate *>(resource).
Some input related code in kwin is mislead by the fact that when the
input region is infinite, SurfaceInterface::input() is going to return
an empty QRegion object.
We cannot really do that because the client could have just set a valid
empty wl_region object to ignore all input events.
This change makes SurfaceInterface assign an actually infinite region
when a NULL input region has been passed to set_input_region().
