Version 3.26.31.8 (merged r21903)

Array.concat: properly go to dictionary mode when required

BUG=chromium:387031
LOG=N
R=danno@chromium.org

Review URL: https://codereview.chromium.org/356503005

git-svn-id: https://v8.googlecode.com/svn/branches/3.26@21981 ce2b1a6d-e550-0410-aec6-3dcde31c8c00