This method is defined only if at least one of the allocators defines
it. If SmallAllocator defines reallocate and b.length <=
threshold && s <= threshold, the call is forwarded to SmallAllocator. If LargeAllocator defines expand and b.length > threshold && s > threshold, the call is forwarded to LargeAllocator. Otherwise, the call returns false.
This method is defined only if at least one of the allocators defines it. If SmallAllocator defines reallocate and b.length <= threshold && s <= threshold, the call is forwarded to SmallAllocator. If LargeAllocator defines expand and b.length > threshold && s > threshold, the call is forwarded to LargeAllocator. Otherwise, the call returns false.