Only make function literals in top-level object literals pretenured and constant function properties.

This change is a refinement of http://code.google.com/p/v8/source/detail?r=7283. Making all
function literals inside object literals constant function properties causes us to lose map
sharing. This hurts code where many object literals are created.

The idea is that top-level code is mostly executed once and functions inside top-level
object literals remain fast with this change.

BUG=v8:1795
Review URL: http://codereview.chromium.org/8746018

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@10096 ce2b1a6d-e550-0410-aec6-3dcde31c8c00