harmony-scoping: Allow 'const' iteration variables in strict mode.

R=rossberg@chromium.org
BUG=v8:2506
LOG=N

Review URL: https://codereview.chromium.org/671913002

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@24834 ce2b1a6d-e550-0410-aec6-3dcde31c8c00
fix build after r24830

TBR=bmeurer@chromium.org

BUG=

Review URL: https://codereview.chromium.org/675733002

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@24835 ce2b1a6d-e550-0410-aec6-3dcde31c8c00