Port r11596 (0cee9fca)

Original commit message:
Array index computation dehoisting.

When an array index (in an array access) is a simple "expression + constant", just embed the constant in the array access operation so that the full index expression is (potentially) no longer used and its live range can be much shorter.
This is effective in conjunction with array bounds check removal (otherwise the index is anyway used in the check).

BUG=
TEST=

Review URL: https://chromiumcodereview.appspot.com/10442003
Patch from Akos Palfi <palfia@homejinni.com>.

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@11644 ce2b1a6d-e550-0410-aec6-3dcde31c8c00