Keep track of which maps are associated with prototype objects so we can tune the fast-case vs. hash map heuristics accordingly.
This is a reland of r11681 https://chromiumcodereview.appspot.com/10448011 , which was reverted because of layout test failures that were actually caused by the long-standing issue fixed in https://chromiumcodereview.appspot.com/10515006 (r11706).
Review URL: https://chromiumcodereview.appspot.com/10532021

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@11727 ce2b1a6d-e550-0410-aec6-3dcde31c8c00