* Return null from VM.mainView if no view exists
* Retry in connectToServiceProtocol if a view is not yet available
* Do not explicitly call exit from the benchmarks - it will not cleanly shut down the engine
- output single-line JSON because iOS 9.x cannot output more than one line
- move the workaround for #7433 into LiveTestWidgetsFlutterBinding so that it works in all cases (e.g. animation_bench.dart on iOS)
