Remove HeapProxy and use the BlockHeapManager by default.

I've run some Dromaeo benchmarks and there's no significant performance difference between the 2 version (it's in the noise of the measure).

BUG=
R=chrisha@chromium.org

Review URL: https://codereview.appspot.com/135780043

git-svn-id: http://sawbuck.googlecode.com/svn/trunk@2281 15e8cca8-e42c-11de-a347-f34a4f72eb7d