https://bugs.webkit.org/show_bug.cgi?id=126556

Reviewed by Geoffrey Garen.

Sweeping happens at an awkward time during collection due to the fact that destructors can 
cause arbitrary reentry into the VM. This patch separates collecting and sweeping, and delays 
sweeping until after collection has completely finished.

* heap/Heap.cpp:
(JSC::Heap::collectAllGarbage):
(JSC::Heap::collect):
(JSC::Heap::collectIfNecessaryOrDefer):
* heap/Heap.h:
* heap/MarkedSpace.cpp:
(JSC::MarkedSpace::sweep):
* runtime/GCActivityCallback.cpp:
(JSC::DefaultGCActivityCallback::doWork):


git-svn-id: http://svn.webkit.org/repository/webkit/trunk@161429 268f45cc-cd09-0410-ab3c-d52691b4dbfc