The API to create a sticky spatial node doesn't allow us to set a clip
chain that will apply to all the contents of the sticky node. This means
that when the ClipManager sets up the clip state for the sticky node,
the clip chain for it is dropped. Everything still works currently
because the contents of the sticky node have their own clip chains whose
parent link will include the sticky node's clip chain. However, in the
next patch we're going to sever that parent link to fix other issues,
and so we will break this mechanism. This patch fixes it up by
explicitly applying the sticky node's clip chain to the stacking context
that contains all the sticky contents. This ensures all those items pick
up the clip chain.
Differential Revision: https://phabricator.services.mozilla.com/D18100
--HG--
extra : moz-landing-system : lando
