Merged r14550 into 3.18 branch.

Fix occasional crash when lithium goes out of vregs.

R=jkummerow@chromium.org
BUG=

Review URL: https://codereview.chromium.org/22634009

git-svn-id: https://v8.googlecode.com/svn/branches/3.18@16123 ce2b1a6d-e550-0410-aec6-3dcde31c8c00