Integrated the ZebraBlockHeap to the BlockHeapManager.

There are some details missing since the HeapManager is not finished yet.

I'm sorry for the delay. I faced not one, but two bugs with
non-deterministic behaviour, most times the tests passed, but a very
few times just failed on random places.
It was difficult to debug since I had no idea where or when it was
going to break.
Those bugs are fixed now, ironically were caused by use after free.
The good part is that now I have a very good idea how everything works
since I had to dig deep to discover the bugs.

BUG=
R=chrisha@chromium.org

Review URL: https://codereview.appspot.com/125510044

git-svn-id: http://sawbuck.googlecode.com/svn/trunk@2272 15e8cca8-e42c-11de-a347-f34a4f72eb7d