Implement platform deleters per spec.

LayoutTests/storage/domstorage/localstorage/delete-removal.html

Index: LayoutTests/storage/domstorage/localstorage/delete-removal.html
diff --git a/LayoutTests/storage/domstorage/localstorage/delete-removal.html b/LayoutTests/storage/domstorage/localstorage/delete-removal.html
index 0eb43fbd53dd98ee4aa7aa1bbefa49737d29dd16..25781b735cf4a71ff5b4119eb8722d6461b5ec07 100644
--- a/LayoutTests/storage/domstorage/localstorage/delete-removal.html
+++ b/LayoutTests/storage/domstorage/localstorage/delete-removal.html
@@ -18,7 +18,7 @@ function runTest()
         return;
     }
     localStorage.clear();
-    
+
     log("foo (before anything) is: " + localStorage.foo);
     localStorage.foo = "bar";
     log("foo (after a named property settter set) is: " + localStorage.foo);
@@ -40,6 +40,11 @@ function runTest()
     log("foo (after an implicit settter set) is: " + localStorage.foo);
     delete localStorage["foo"];
     log("foo (after an indexed delete) is: " + localStorage.foo);
+
+    Object.defineProperty(localStorage, "bar", {value: "present", configurable: true});
+    log("bar (before an indexed delete) is present: " + ("bar" in localStorage));
+    delete localStorage["bar"];
+    log("bar (after an indexed delete) is present: " + ("bar" in localStorage));
 }
 
 </script>