Remove a race between sweepers and the free space skipping code (while iterating new space pointers)

Remove a race between sweepers and the free space skipping code (while iterating new space pointers).

There has been a race between a sweeper setting the next pointer on
free list node and the main thread skipping free space during update of
new space pointers in the heap.

This change removes the free space skipping code.

R=hpayer@chromium.org
BUG=370551
LOG=N

Committed: https://code.google.com/p/v8/source/detail?r=21306

[Hannes Payer (out of office), 2014-05-14 11:32:06]

LGTM if it does not tank performance.

Can we describe in the subject what the CL actually does. Right now it is pretty
ambiguous.

[Jarin, 2014-05-14 12:35:26]

Committed patchset #1 manually as r21306 (presubmit successful).