Use DOMSettableTokenList for {HTMLAnchorElement, HTMLAreaElement}.ping.

LayoutTests/fast/dom/ping-attribute-dom-binding.html

Index: LayoutTests/fast/dom/ping-attribute-dom-binding.html
diff --git a/LayoutTests/fast/dom/ping-attribute-dom-binding.html b/LayoutTests/fast/dom/ping-attribute-dom-binding.html
index b49b846c52d3b7b3dfff7f5bf3b00e6f5cf1086f..faea097d8661ca7865202ec6c712fb5383d65b9f 100644
--- a/LayoutTests/fast/dom/ping-attribute-dom-binding.html
+++ b/LayoutTests/fast/dom/ping-attribute-dom-binding.html
@@ -9,24 +9,24 @@
 description('Tests the DOM bindings for the ping attribute');
 
 var anchor = document.createElement('a');
-shouldBeEqualToString('anchor.ping', '');
+shouldBe('anchor.ping', '[]');
 anchor.setAttribute('ping', 'p1');
-shouldBeEqualToString('anchor.ping', 'p1');
+shouldBe('anchor.ping', '["p1"]');
 anchor.ping = 'p2';
 shouldBeEqualToString('anchor.getAttribute("ping")', 'p2');
 anchor.ping = null;
 shouldBeEqualToString('anchor.getAttribute("ping")', 'null');
-shouldBeEqualToString('anchor.ping', 'null');
+shouldBe('anchor.ping', '["null"]');
 
 var area = document.createElement('area');
-shouldBeEqualToString('area.ping', '');
+shouldBe('area.ping', '[]');
 area.setAttribute('ping', 'p1');
-shouldBeEqualToString('area.ping', 'p1');
+shouldBe('area.ping', '["p1"]');
 area.ping = 'p2';
 shouldBeEqualToString('area.getAttribute("ping")', 'p2');
 area.ping = null;
 shouldBeEqualToString('area.getAttribute("ping")', 'null');
-shouldBeEqualToString('area.ping', 'null');
+shouldBe('area.ping', '["null"]');
 

[tkent, 2015/07/14 00:29:44]

Please add tests for DOMTokenList functions such as anchor.ping.add(), remove(),
...

 </script>
 </body>