Implementation for this case

var x = {};
x.__defineGetter__("y", function Y() { return 42; });

BUG=v8:1818
TEST=cctest/test-heap-profiler/FastCaseGetter

Review URL: http://codereview.chromium.org/8491041
Patch from Ilya Tikhonovsky <loislo@chromium.org>.

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@9985 ce2b1a6d-e550-0410-aec6-3dcde31c8c00