https://bugs.webkit.org/show_bug.cgi?id=87039

Reviewed by Darin Adler.

../JavaScriptCore: 

This helps avoid OOM crashes on small platforms, and helps avoid "too much GC"
performance issues on big platforms.

* heap/Heap.cpp:
(JSC::Heap::Heap):
(JSC::Heap::collect):
* heap/Heap.h:
(Heap): GC balances between a fixed minimum and a proportional multiplier,
which are limited based on system RAM.

* runtime/JSGlobalData.cpp:
(JSC::JSGlobalData::JSGlobalData):
(JSC::JSGlobalData::createContextGroup):
(JSC::JSGlobalData::create):
(JSC::JSGlobalData::createLeaked):
* runtime/JSGlobalData.h:
(JSGlobalData): Renamed HeapSize to HeapType because the exact size is
influenced by the heap type, but not determined by it.

../WTF: 

Added a helper function for measuring system RAM.

* GNUmakefile.list.am:
* WTF.gypi:
* WTF.pro:
* WTF.vcproj/WTF.vcproj:
* WTF.xcodeproj/project.pbxproj:
* wtf/AmountOfRAM.cpp: Added.
(WTF):
(WTF::computeAmountOfRAM):
(WTF::amountOfRAM):
* wtf/AmountOfRAM.h: Added.
(WTF):
* wtf/CMakeLists.txt:
* wtf/StdLibExtras.h:
(WTF):


git-svn-id: http://svn.webkit.org/repository/webkit/trunk@118019 268f45cc-cd09-0410-ab3c-d52691b4dbfc