7003860: G1: assert(_cur_alloc_region == NULL || !expect_null_cur_alloc_region) fails Summary: Wrong assumption about expecting the current alloc region expected to be NULL in expand_and_allocate(). Reviewed-by: brutisso, ysr

6983204: G1: Nightly test nsk/regression/b4958615 failing with +ExplicitGCInvokesConcurrent Summary: Enable reference discovery during concurrent marking by setting the reference processor field of the concurrent marking closure. Keep reference objects on the discovered reference lists alive during incremental evacuation pauses until they are processed at the end of concurrent marking. Reviewed-by: ysr, tonyp