[Qt] Implement IncrementalSweeper and HeapTimer
https://bugs.webkit.org/show_bug.cgi?id=103996

Reviewed by Simon Hausmann.

Implements the incremental sweeping garbage collection for the Qt platform.

* heap/HeapTimer.cpp:
(JSC::HeapTimer::HeapTimer):
(JSC::HeapTimer::~HeapTimer):
(JSC::HeapTimer::timerEvent):
(JSC::HeapTimer::synchronize):
(JSC::HeapTimer::invalidate):
(JSC::HeapTimer::didStartVMShutdown):
* heap/HeapTimer.h:
(HeapTimer):
* heap/IncrementalSweeper.cpp:
(JSC::IncrementalSweeper::IncrementalSweeper):
(JSC::IncrementalSweeper::scheduleTimer):
* heap/IncrementalSweeper.h:
(IncrementalSweeper):

git-svn-id: http://svn.webkit.org/repository/webkit/trunk@141089 268f45cc-cd09-0410-ab3c-d52691b4dbfc