Add basic infrastructure for protecting V8's heap when leaving the VM

Add basic infrastructure for protecting V8's heap when leaving the VM
and unprotecting it when (re)entering.  The functionality is enabled
by the flag --protect-heap and requires V8 to be built with
ENABLE_HEAP_PROTECTION and ENABLE_LOGGING_AND_PROFILING defined.

Implemented on Linux and Windows but not yet for other platforms.

Review URL: http://codereview.chromium.org/53004

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@1595 ce2b1a6d-e550-0410-aec6-3dcde31c8c00