When under a load, the ProfilerEventsProcessor thread can start
(enter Run) after Stop has been called, thus resetting running_
data member back to 'true', and starting an infinite loop.

BUG=833

Review URL: http://codereview.chromium.org/3157022

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@5304 ce2b1a6d-e550-0410-aec6-3dcde31c8c00