Fix IdleNotification to correctly free objects.

Fix IdleNotification to correctly free objects.

Heap::IdleNotification doesn't free all objects
in special cases since incremental marking is enabled.

Use the slower precise sweeper in the last phase of
Heap::IdleNotification.

Patch by Peter Varga

BUG=none
TEST=cctest/test-api/IdleNotificationForceGC

[Vyacheslav Egorov (Chromium), 2011-11-09 16:11:32]

I am not sure we want IdleNotification to force V8 abandon incremental marking
and do a full GC from the scratch.

I think if embedder wants V8 to shrink the heap he should use
LowMemoryNotification.

[Peter Varga, 2011-11-09 16:25:47]

Thank you for the quick answer.
The LowMemoryNotification is exactly what I need.