This allows to profile "unresponsive" web pages in the same way
as it is possible to break into them with the debugger.

BUG=http://code.google.com/p/chromium/issues/detail?id=28689

Review URL: http://codereview.chromium.org/450011

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@3382 ce2b1a6d-e550-0410-aec6-3dcde31c8c00