Re-enable evacuation of recently allocated regions

Reduces RAM since these regions usually have a low live % per
the generational hypothesis. Since these get collected earlier it
means the average heap size goes down.

60s after booting N6P CC before (average of 8 samples):
Dalvik .Heap PSS system wide: 28711K

After:
Dalvik .Heap PSS system wide: 18757.5K

EAAC: 1305 -> 1274 (30 samples)

Test: test-art-host CC baker and debug phone bootin

Bug: 12687968
Bug: 30124683

Change-Id: I30465be4525855ee3b78e6fafa5577a78d365bf4