https://bugs.webkit.org/show_bug.cgi?id=97618

Reviewed by Filip Pizlo.

Added an option to dump object size inference statistics.

To see statistics on live objects:

    jsc --showHeapStatistics=1

To see cumulative statistics on all objects ever allocated:

    jsc --showHeapStatistics=1 --objectsAreImmortal=1

    (This is useful for showing GC churn caused by over-allocation.)

To support this second mode, I refactored Zombies to separate out their
immortality feature so I could reuse it.

* heap/Heap.cpp:
(JSC::MarkObject): Helper for making things immortal. We have to checked
for being zapped because blocks start out in this state.

(JSC::StorageStatistics): Gather statistics by walking the heap. Ignore
arrays and hash tables for now because they're not our focus. (We'll
remove these exceptions in future.)

(JSC::Heap::collect): Moved zombify to the end so it wouldn't interfere
with statistics gathering.

(JSC::Heap::showStatistics):
(JSC::Heap::markAllObjects): Factored out helper, so statistics could
take advantage of immortal objects.

(Zombify): Don't mark immortal objects -- that's another class's job now.

(JSC::Zombify::operator()):
(JSC::Heap::zombifyDeadObjects): Take advantage of forEachDeadCell instead
of rolling our own.

* heap/Heap.h:
(Heap):
* heap/MarkedSpace.h:
(MarkedSpace):
(JSC::MarkedSpace::forEachDeadCell): Added, so clients don't have to do
the iteration logic themselves.

* runtime/Options.cpp:
(JSC::Options::initialize):
* runtime/Options.h: New options, listed above. Make sure to initialize
based on environment variable first, so we can override with specific settings.


git-svn-id: http://svn.webkit.org/repository/webkit/trunk@129586 268f45cc-cd09-0410-ab3c-d52691b4dbfc