https://bugs.webkit.org/show_bug.cgi?id=85429

We shouldn't have to wait for the opportunistic GC timer to fire in order 
to call object destructors. Instead, we should incrementally sweep some 
subset of the blocks requiring sweeping periodically. We tie this sweeping 
to a timer rather than to collections because we want to reclaim this memory 
even if we stop allocating. This way, our memory usage scales smoothly with 
actual use, regardless of whether we've recently done an opportunistic GC or not.

Reviewed by Geoffrey Garen.

* CMakeLists.txt:
* GNUmakefile.list.am:
* JavaScriptCore.gypi:
* JavaScriptCore.vcproj/JavaScriptCore/JavaScriptCore.vcproj:
* JavaScriptCore.xcodeproj/project.pbxproj:
* Target.pri:
* heap/Heap.cpp:
(JSC::Heap::Heap):
(JSC::Heap::collect): We no longer sweep during a full sweep. We only shrink now,
which we will switch over to being done during incremental sweeping too as soon as
all finalizers can be run lazily (and, by extension, incrementally). 
(JSC::Heap::sweeper):
(JSC):
* heap/Heap.h:
(JSC):
(Heap):
* heap/IncrementalSweeper.cpp: Added.
(JSC):
(JSC::IncrementalSweeper::timerDidFire): The IncrementalSweeper works very similarly to 
GCActivityCallback. It is tied to a run-loop based timer that fires periodically based 
on how long the previous sweep increment took to run. The IncrementalSweeper doesn't do 
anything if the platform doesn't support CoreFoundation.
(JSC::IncrementalSweeper::IncrementalSweeper):
(JSC::IncrementalSweeper::~IncrementalSweeper):
(JSC::IncrementalSweeper::create):
(JSC::IncrementalSweeper::scheduleTimer):
(JSC::IncrementalSweeper::cancelTimer):
(JSC::IncrementalSweeper::doSweep): Iterates over the snapshot of the MarkedSpace taken 
during the last collection, checking to see which blocks need sweeping. If it successfully 
gets to the end of the blocks that need sweeping then it cancels the timer.
(JSC::IncrementalSweeper::startSweeping): We take a snapshot of the Heap and store it in 
a Vector that the incremental sweep will iterate over. We also reset our index into this Vector.
* heap/IncrementalSweeper.h: Added.
(JSC):
(IncrementalSweeper):
* heap/MarkedBlock.h:
(JSC::MarkedBlock::needsSweeping): If a block is in the Marked state it needs sweeping 
to be usable and to run any destructors that need to be run.


git-svn-id: http://svn.webkit.org/repository/webkit/trunk@119028 268f45cc-cd09-0410-ab3c-d52691b4dbfc