G1 Initializes and validates MaxGCPauseMillis and GCPauseIntervalMillis in the constructor of G1CollectorPolicy.
This should be moved to Arguments::set_g1_gc_flags, where other default values of globally known flags are set.
We can then move the constraint checking to the proper command line flag constraint functions (pause interval > pause target and setting pause interval without setting pause target) and modify the constraints so that they are applied before the GC subsystem is initialized (by changing AfterMemorInit to AfterErgo)