Avoid HeapObject check in HStoreNamedField.

This way an HStoreNamedField instruction can never deoptimize
itself, which is another important step towards a working
store elimination.

R=jarin@chromium.org

Review URL: https://codereview.chromium.org/299373005

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@21509 ce2b1a6d-e550-0410-aec6-3dcde31c8c00
Fix d8's interactive shell.

R=danno@chromium.org

Review URL: https://codereview.chromium.org/305553002

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@21510 ce2b1a6d-e550-0410-aec6-3dcde31c8c00