There is new code in defNewGeneration.cpp:

hg log defNewGeneration.cpp | more
changeset: 9816:756bb5cfc5cb
user: sangheki
date: Tue Jan 05 17:05:13 2016 -0800
summary: 8144527: NewSizeThreadIncrease would make an overflow

The problem is probably here if threads_count is 0:

    if (NewSizeThreadIncrease <= max_uintx / threads_count) {