Enable large object space for zygote.

Enable large object space for zygote.

We now enable the large object space before the zygote fork.
This reduces the size of the zygote and removes the need for
excessive explicit GCs during phone booting.

Changed the card set mod union table to support forgetting cards.
If a card has no non null references which are in another space
then it is removed from the set.

Added logging of the zygote size when you do a SIGQUIT.

Dalvik PSS is the same or slightly lower (1-3%).

Zygote space size:
Before: 15MB
After: 8MB (+ some large objects).

TODO: Combine remembered sets and mod union tables into a single
interface.

Bug: 16398684
Change-Id: Ie48cdf35004a0a37eedb1ccc1bf214b1fa9e0cca