Instead of globally tracking allocated space limits, which was
not implemented properly anyway (i.e. lack of synchronization
on the reading side), track it per MemoryAllocator (that is
per heap/isolate).

In particular, avoid to call IsBadWritePtr() on Windows, it is
obsolete and Microsoft strongly discourages its usage.

R=mstarzinger@chromium.org

Review URL: https://codereview.chromium.org/23903008

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@16542 ce2b1a6d-e550-0410-aec6-3dcde31c8c00