I have several Chromium's core files having SIGPROF signal handler called in the context of an arbitrary thread, causing a crash. This change introduces checking of current thread in the signal handler.

Review URL: http://codereview.chromium.org/171115

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@2825 ce2b1a6d-e550-0410-aec6-3dcde31c8c00