Use unsigned integer arithmetic in Zone::NewExpand.

Use unsigned integer arithmetic in Zone::NewExpand.

BUG=328202
R=jkummerow@chromium.org
LOG=N

Committed: https://code.google.com/p/v8/source/detail?r=18564

[Dmitry Lomov (no reviews), 2013-12-16 12:51:30]

PTAL. 
In some other CL, we might want to switch the entire Zone to size_t

[Jakob Kummerow, 2013-12-16 15:30:34]

There's definitely a whole lot more that we should clean up long-term, but this
LGTM for now.

https://codereview.chromium.org/108783005/diff/1/src/zone.cc
File src/zone.cc (right):

https://codereview.chromium.org/108783005/diff/1/src/zone.cc#newcode181
src/zone.cc:181: ASSERT(size > limit_ - position_);
this subtraction is undefined behavior too

https://codereview.chromium.org/108783005/diff/1/src/zone.cc#newcode230
src/zone.cc:230: ASSERT(position_ <= limit_);
this comparison is undefined behavior too

[Dmitry Lomov (no reviews), 2013-12-17 10:27:28]

On 2013/12/16 15:30:34, Jakob wrote:
> There's definitely a whole lot more that we should clean up long-term, but
this
> LGTM for now.
> 
> https://codereview.chromium.org/108783005/diff/1/src/zone.cc
> File src/zone.cc (right):
> 
> https://codereview.chromium.org/108783005/diff/1/src/zone.cc#newcode181
> src/zone.cc:181: ASSERT(size > limit_ - position_);
> this subtraction is undefined behavior too
> 
> https://codereview.chromium.org/108783005/diff/1/src/zone.cc#newcode230
> src/zone.cc:230: ASSERT(position_ <= limit_);
> this comparison is undefined behavior too

Agreed, but as discussed offline eliminating address arithmetic is whole
different kettle of fish.

[Dmitry Lomov (no reviews), 2014-01-13 13:00:16]

Committed patchset #1 manually as r18564 (presubmit successful).