Make JSC have a mini mode that kicks in when the JIT is disabled

Make JSC have a mini mode that kicks in when the JIT is disabled
https://bugs.webkit.org/show_bug.cgi?id=185931

Reviewed by Mark Lam.

Source/JavaScriptCore:

This patch makes JSC have a mini VM mode. This currently only kicks in
when the process can't JIT. Mini VM now means a few things:
- We always use a 1.27x heap growth factor. This number was the best tradeoff
  between memory use progression and time regression in run-testmem. We may
  want to tune this more in the future as we make other mini VM changes.
- We always sweep synchronously.
- We disable generational GC.

I'm going to continue to extend what mini VM mode means in future changes.

This patch is a 50% memory progression and an ~8-9% time regression
on run-testmem when running in mini VM mode with the JIT disabled.

* heap/Heap.cpp:
(JSC::Heap::collectNow):
(JSC::Heap::finalize):
(JSC::Heap::useGenerationalGC):
(JSC::Heap::shouldSweepSynchronously):
(JSC::Heap::shouldDoFullCollection):
* heap/Heap.h:
* runtime/Options.h:
* runtime/VM.cpp:
(JSC::VM::isInMiniMode):
* runtime/VM.h:

Tools:

This renames a variable for clarity.

* Scripts/run-testmem:

git-svn-id: https://svn.webkit.org/repository/webkit/trunk@232210 268f45cc-cd09-0410-ab3c-d52691b4dbfc