Removing the former was basically a consequence of removing the latter. The net
effect is, apart from less code, that the signal sender thread is much more
explicit about its logic now.

Review URL: https://codereview.chromium.org/11543020

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@13212 ce2b1a6d-e550-0410-aec6-3dcde31c8c00