The caching code used to require that all keys in the literal were symbol strings
in order to be able to cache object literal maps.

Relaxed this requirement to allow array indices as well (as in { "1": "one", two: "two" }).

Changed the way 'number_of_properties' is calculated so that redundant property slots are not
allocated for array indices. 


Review URL: http://codereview.chromium.org/2858064

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@5114 ce2b1a6d-e550-0410-aec6-3dcde31c8c00