Re-land "Add methods to enable configuration of ResourceConstraints based on limits derived at runtime."

Adds ConfigureResourceConstraintsForCurrentPlatform and SetDefaultResourceConstraintsForCurrentPlatform which configure the heap based on the available physical memory, rather than hard-coding by platform as previous. This change also adds OS::TotalPhysicalMemory to platform.h.

The re-land fix the performance regression caused by accidental change in default max young space size.

BUG=292928
R=hpayer@chromium.org

Review URL: https://codereview.chromium.org/24989003

Patch from Ross McIlroy <rmcilroy@chromium.org>.

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@16983 ce2b1a6d-e550-0410-aec6-3dcde31c8c00