Only JSLoadProperty/JSStoreProperty nodes with external typed arrays can
be lowered to LoadElement/StoreElement, because lowering of non-external
typed arrays would require a map check.

TEST=cctest,unittests,mjsunit
R=svenpanne@chromium.org

Review URL: https://codereview.chromium.org/631093003

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@24426 ce2b1a6d-e550-0410-aec6-3dcde31c8c00