My question means: where in the code you miss a reference to ApplicationSystem? I also preempt the answer, Crosswalk object is widely accessible to solve this issue for you (just get the app_system() from it) in cases that you do not have other option. I fail to see the need of ApplicationSystem being a singleton in the context of this series.

By the way, I even considered making Crosswalk object implement the ContentMainDelegate interface, but avoided to cause less confusion.