Only extend storage if FIELD

R=jkummerow@chromium.org

Review URL: https://chromiumcodereview.appspot.com/16818014

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@15125 ce2b1a6d-e550-0410-aec6-3dcde31c8c00
Refactor turning polymorphic loads into monomorphic loads
- remove special code for polymorphic loading of array length
- use it in VisitCountOperation

BUG=
R=hpayer@chromium.org

Review URL: https://chromiumcodereview.appspot.com/16948005

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@15126 ce2b1a6d-e550-0410-aec6-3dcde31c8c00