MIPS64: Unbreak build after r23579.

TEST=
BUG=
R=balazs.kilvady@imgtec.com, bmeurer@chromium.org

Review URL: https://codereview.chromium.org/531743002

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@23608 ce2b1a6d-e550-0410-aec6-3dcde31c8c00
Fix imports in test runner.

TBR=bmeurer@chromium.org

Review URL: https://codereview.chromium.org/532693002

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@23609 ce2b1a6d-e550-0410-aec6-3dcde31c8c00
Lower simplified StringAdd to stub call.

R=titzer@chromium.org
TEST=cctest/test-simplified-lowering/LowerStringOps_to_calls

Review URL: https://codereview.chromium.org/530973002

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@23610 ce2b1a6d-e550-0410-aec6-3dcde31c8c00