In the process, add shared stubs for DictionaryValue lookups that are handled in the same way as fast elements and external array elements.

Includes code for MIPS, which compiles and run polymorph-arrays.js successfully.

R=jkummerow@chromium.org
BUG=none
TEST=test/mjsunit/polymorph-arrays.js

Review URL: http://codereview.chromium.org/7227010

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@8579 ce2b1a6d-e550-0410-aec6-3dcde31c8c00