https://bugs.webkit.org/show_bug.cgi?id=117948

Reviewed by Geoffrey Garen.

Source/JavaScriptCore:

Currently just count strings. Strings get counted in such a way that we won't re-count strings
that are aliased, by dividing by the reference count. This then ups the GC footprint and allows
the collector to appropriately amortize itself.

* heap/Heap.cpp:
(JSC::Heap::Heap):
(JSC::Heap::size):
(JSC::Heap::collect):
* heap/Heap.h:
(Heap):
* heap/SlotVisitor.h:
* heap/SlotVisitorInlines.h:
(JSC::SlotVisitor::reportExtraMemoryUsage):
(JSC):
* runtime/JSString.cpp:
(JSC::JSString::visitChildren):

Source/WTF:

Expose some functionality needed for properly measuring StringImpl footprint.

* wtf/Atomics.h:
(WTF::weakCompareAndSwapSize):
(WTF):
* wtf/MathExtras.h:
(divideRoundedUp):
* wtf/text/StringImpl.h:
(WTF::StringImpl::cost):
(StringImpl):
(WTF::StringImpl::costDuringGC):
(WTF::StringImpl::refCount):

git-svn-id: http://svn.webkit.org/repository/webkit/trunk@153247 268f45cc-cd09-0410-ab3c-d52691b4dbfc