Extension to https://bugs.webkit.org/show_bug.cgi?id=70442, we now have to add support for tracking property changes for subclasses of CCLayerImpl. This is necessary for correct damage tracking of special layer types such as plugin layers.
Closing this bug; there have been enough ancillary bug-fixes related to damage tracking on specific layer types, that I have more confidence this is actually not an issue.
If it ends up being an issue, it will be appropriate to deal with it on a case-by-case basis, anyway.
+cc to backer in case he has something to say.