Allow boundscheck elimination to work on Smi keys.

R=jkummerow@chromium.org

Review URL: https://chromiumcodereview.appspot.com/16035016

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@15001 ce2b1a6d-e550-0410-aec6-3dcde31c8c00
Baseline for-of implementation

Add full-codegen support for the ES6 for-of iteration statement.

R=mstarzinger@chromium.org, rossberg@chromium.org
TEST=mjsunit/harmony/iteration-semantics
BUG=v8:2214

Review URL: https://codereview.chromium.org/15288011

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@15002 ce2b1a6d-e550-0410-aec6-3dcde31c8c00