Changes include:
- completed concurrent OSR tasks trigger a stack check interrupt.
- polling for completion is now guarded by a stack check.
- circular buffer for completed OSR tasks instead of list.

R=titzer@chromium.org
BUG=

Review URL: https://codereview.chromium.org/24237009

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@16934 ce2b1a6d-e550-0410-aec6-3dcde31c8c00