https://retrace.fedoraproject.org/faf/problems/bthash/?bth=2c9e4b335a4f17dea5e095f0a3e8f79aa40943cb

Clearly it's a really bad idea to own these objects at shutdown, so
instead use weak references, and also ensure that the
CanvasUpdateRequester is not deleted before the event is dispatched
just in case.

Change-Id: Iee8a109fe5969b2a3345e0ef266aee014962ae57