Try to simplify the semantics of the profiling code by making

Try to simplify the semantics of the profiling code by making
sure to suspend the thread (if necessary) on mac/win32 before
reading the VM state.

Avoid dealing with signals delivered to non-VM threads on
linux no matter if we're profiling or not.
Review URL: http://codereview.chromium.org/3845006

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@5641 ce2b1a6d-e550-0410-aec6-3dcde31c8c00