These are likely causing some of the flaky crashes in Object.observe code. I've reorganized some of the code to minimize the number of necessary calls to map() (by saving the result of map()->is_observed() in a local bool).

Also move down an unnecessarily early call to Uint32ToString when sending an element deletion notification.

Review URL: https://chromiumcodereview.appspot.com/11316202

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@13070 ce2b1a6d-e550-0410-aec6-3dcde31c8c00