Eliminate further write barriers for old space allocations.

Eliminate further write barriers for old space allocations.

Storing a map or an immortal immovable object to old space
allocations requires no write barriers if the object is the
new space dominator.

R=hpayer@chromium.org, mstarzinger@chromium.org

Committed: https://code.google.com/p/v8/source/detail?r=21216

[Benedikt Meurer, 2014-05-09 11:51:33]

Almost no more write barriers in pretenured GeneratePayloadTree... :-)

[Hannes Payer (out of office), 2014-05-09 11:58:02]

lgtm

[Michael Starzinger, 2014-05-09 12:06:26]

LGTM.

[Benedikt Meurer, 2014-05-09 12:06:54]

Committed patchset #1 manually as r21216 (presubmit successful).