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