Fix a bug in %_GetCachedArrayIndex.
Fix a bug in %_GetCachedArrayIndex.

This inline runtime function had the wrong super class.
It did not cause any problems since it is only used in
our natives and never in a test context.
Review URL: http://codereview.chromium.org/7253004

git-svn-id: b158db1e4b4ab85d4c9e510fdef4b1e8c614b15b@8441 ce2b1a6d-e550-0410-aec6-3dcde31c8c00

UniversalFuture/moosh,UniversalFuture/moosh,UniversalFuture/moosh,UniversalFuture/moosh