Fix CopyCode to properly record object pointer writes.

Fix CopyCode to properly record object pointer writes.

R=mstarzinger@chromium.org

[Michael Starzinger, 2013-05-14 16:43:10]

https://codereview.chromium.org/14587008/diff/1/src/heap.cc
File src/heap.cc (right):

https://codereview.chromium.org/14587008/diff/1/src/heap.cc#newcode3867
src/heap.cc:3867: incremental_marking()->RecordWrites(new_code);
So I looked into this write-barrier and I don't think we need one here. The
reasons for this are the following ...

1) All objects reachable from the code object header are pretenured and hence
cannot be in new-space. That's why the assertion in Heap::RecordWrites that the
address is not in code-space makes sense.

2) The newly allocated code object is guaranteed to still be white after we
copied over it's contents. So we couldn't have introduced black-to-white
pointers with the block copy.

3) The newly allocated code object will eventually be scanned by the marker
before a GC (it's still white) and hence all slots that point into evacuation
candidates will be discovered.