Merged r14614, r15489 into 3.18 branch.

Skip flaky regress-crbug-160010 regression test.

MIPS: Fix bug in StringConstructCode builtin.

BUG=chromium:160010

R=jkummerow@chromium.org

Review URL: https://codereview.chromium.org/19058003

git-svn-id: https://v8.googlecode.com/svn/branches/3.18@15662 ce2b1a6d-e550-0410-aec6-3dcde31c8c00