Implement high promotion mode for new space.

Implement high promotion mode for new space.

This mode drastically decreases pause times by limiting maximum capacity
of the young generation when mutators generate many long-lived objects.
It shrinks new space back to the initial capacity and keeps it at that
capacity until survival rate decreases again.

R=erik.corry@gmail.com

Committed: http://code.google.com/p/v8/source/detail?r=10072

[Michael Starzinger, 2011-11-25 13:26:08]

PTAL.

[Erik Corry, 2011-11-25 14:38:29]

LGTM