[V8] Remove V8GCController::m_edenNodes and make minor DOM GC more precise
https://bugs.webkit.org/show_bug.cgi?id=108579

Reviewed by Adam Barth.

Currently V8GCController::m_edenNodes stores a list of nodes whose
wrappers have been created since the latest GC. The reason why we
needed m_edenNodes is that there was no way to know a list of wrappers
in the new space of V8. By using m_edenNodes, we had been approximating
'wrappers in the new space' by 'wrappers that have been created since
the latest GC'.

Now V8 provides VisitHandlesForPartialDependence(), with which WebKit
can know a list of wrappers in the new space. By using the API, we can
remove V8GCController::m_edenNodes. The benefit is that (1) we no longer
need to keep m_edenNodes and that (2) it enables more precise minor
DOM GC (Remember that m_edenNodes was just an approximation).

Performance benchmark: https://bugs.webkit.org/attachment.cgi?id=185940
The benchmark runs 300 iterations, each of which creates 100000 elements.
The benchmark measures average, min, median, max and stdev of execution times
of the 300 iterations. This will tell us the worst-case overhead of this change.

Before:
  mean=59.91ms, min=39ms, median=42ms, max=258ms, stdev=47.48ms

After:
  mean=58.75ms, min=35ms, median=41ms, max=250ms, stdev=47.32ms

As shown above, I couldn't observe any performance regression.

No tests. No change in behavior.

* bindings/v8/DOMDataStore.h:
(WebCore::DOMDataStore::setWrapperInObject):
* bindings/v8/DOMWrapperWorld.h:
(DOMWrapperWorld):
(WebCore::DOMWrapperWorld::getWorldWithoutContextCheck):
* bindings/v8/V8Binding.h:
(WebCore):
(WebCore::worldForEnteredContextIfIsolated):
(WebCore::worldForEnteredContextWithoutContextCheck):
* bindings/v8/V8DOMWindowShell.cpp:
(WebCore::V8DOMWindowShell::initializeIfNeeded):
* bindings/v8/V8GCController.cpp:
(WebCore::gcTree):
(WebCore):
(MinorGCWrapperVisitor):
(WebCore::MinorGCWrapperVisitor::MinorGCWrapperVisitor):
(WebCore::MinorGCWrapperVisitor::notifyFinished):
(WebCore::MajorGCWrapperVisitor::MajorGCWrapperVisitor):
(WebCore::V8GCController::gcPrologue):
(WebCore::V8GCController::minorGCPrologue):
(WebCore::V8GCController::majorGCPrologue):
* bindings/v8/V8GCController.h:
(V8GCController):

git-svn-id: http://svn.webkit.org/repository/webkit/trunk@142419 268f45cc-cd09-0410-ab3c-d52691b4dbfc