Release evacuation candidates after parallel sweeper threads completed.

BUG=

Review URL: https://codereview.chromium.org/12082101

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@13708 ce2b1a6d-e550-0410-aec6-3dcde31c8c00
Heap snapshot doesn't detect the fact that an old object was overriden by new one.

It is a test only patch. I have no solution yet.

BUG=V8:2189
TEST=

Review URL: https://chromiumcodereview.appspot.com/12321042

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@13709 ce2b1a6d-e550-0410-aec6-3dcde31c8c00