Function realloc 

pub unsafe fn realloc(
    ptr: *mut u8,
    layout: Layout,
    new_size: usize,
) -> Option<NonNull<u8>>

Fallible reallocation matching standard alloc interface.

Safety

• ptr is allocated via this allocator,
• layout is the same layout that was used to allocate that block of memory,
• new_size is greater than zero,
• new_size, when rounded up to the nearest multiple of layout.align(), does not overflow isize.