Merge r10187, r10188 from the bleeding_edge to the 3.7 branch.

Merge r10187, r10188 from the bleeding_edge to the 3.7 branch.

Rescan cells at the end of mark-sweep.  This means they don't need a
write barrier.
Review URL: http://codereview.chromium.org/8816021
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Remove write barriers for cells on x64, ARM and MIPS.
Review URL: http://codereview.chromium.org/8834005
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Committed: http://code.google.com/p/v8/source/detail?r=10392

[Michael Starzinger, 2012-01-11 15:33:44]

LGTM.