The checking for strings when performing binary add was missing on x64 and ARM. This is a prerequisite for adding string add in generated code for these two platforms.
Review URL: http://codereview.chromium.org/465028

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@3416 ce2b1a6d-e550-0410-aec6-3dcde31c8c00