Cache result of ScriptNameOrSourceURL function. The function is quite slow on large(several MBs) scripts which causes significant slowdown when capturing stack trace for such scripts.
Review URL: https://chromiumcodereview.appspot.com/9564012

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@10902 ce2b1a6d-e550-0410-aec6-3dcde31c8c00