Merged r15914 into trunk branch.

MIPS: Fix debug mode webkit failures.

BUG=v8:2808

R=jkummerow@chromium.org

Review URL: https://codereview.chromium.org/21425002

git-svn-id: https://v8.googlecode.com/svn/trunk@15995 ce2b1a6d-e550-0410-aec6-3dcde31c8c00