DOMException toString is not correct

LayoutTests/fast/dom/script-tests/dataset.js

 description("This tests element.dataset.");
 
 function testGet(attr, expected)
 {
     var d = document.createElement("div");
     d.setAttribute(attr, "value");
     return d.dataset[expected] == "value";
 }
 
 shouldBeTrue("testGet('data-foo', 'foo')");
@@ skipping 34 matching lines @@
 
 shouldBeTrue("testSet('foo', 'data-foo')");
 shouldBeTrue("testSet('fooBar', 'data-foo-bar')");
 shouldBeTrue("testSet('-', 'data--')");
 shouldBeTrue("testSet('Foo', 'data--foo')");
 shouldBeTrue("testSet('-Foo', 'data---foo')");
 shouldBeTrue("testSet('', 'data-')");
 shouldBeTrue("testSet('\xE0', 'data-\xE0')");
 debug("");
 
-shouldThrow("testSet('-foo', 'dummy')", "'Error: SyntaxError: DOM Exception 12'");
-shouldThrow("testSet('foo\x20', 'dummy')", "'Error: InvalidCharacterError: DOM Exception 5'");
-shouldThrow("testSet('foo\uF900', 'dummy')", "'Error: InvalidCharacterError: DOM Exception 5'");
+shouldThrow("testSet('-foo', 'dummy')", "'SyntaxError: An invalid or illegal string was specified.'");
+shouldThrow("testSet('foo\x20', 'dummy')", "'InvalidCharacterError: An invalid or illegal character was specified, such as in an XML name.'");
+shouldThrow("testSet('foo\uF900', 'dummy')", "'InvalidCharacterError: An invalid or illegal character was specified, such as in an XML name.'");
 debug("");
 
 function testDelete(attr, prop)
 {
     var d = document.createElement("div");
     d.setAttribute(attr, "value");
     delete d.dataset[prop];
     return d.getAttribute(attr) != "value";
 }
 
@@ skipping 55 matching lines @@
 shouldBeUndefined("delete div.dataset.Bar; div.dataset.Bar");
 
 debug("");
 debug("Set null:");
 
 var d = document.createElement("div");
 d.dataset.foo = null;
 shouldBe("d.dataset.foo", "'null'");
 
 debug("");