Inline Array.shift() fast path instead of using a code stub.

TEST=mjsunit/array-shift,mjsunit/array-shift2,mjsunit/array-shift3
R=yangguo@chromium.org

Review URL: https://codereview.chromium.org/308793010

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@21592 ce2b1a6d-e550-0410-aec6-3dcde31c8c00