Bug: rdar://problem/4465598 REGRESSION (TOT): Crash occurs at http://maps.google.com/?output=html ( KJS::Identifier::add(KJS::UString::Rep*)

This cause for this bug was that the code to save the window object's property map tried to use the deleted property sentinel key as a normal pointer.

To run this test in Safari:

1. Click here to do a back/forward navigation.
2. You should not crash.

When the automated version of this test passes, you'll see a PASS message below. (The automated version is currently disabled because DumpRenderTree doesn't work with the back/forward cache enabled.)