Make the setCustomValidity() error argument not nullable

LayoutTests/fast/dom/setCustomValidity-validationMessage-expected.txt

Index: LayoutTests/fast/dom/setCustomValidity-validationMessage-expected.txt
diff --git a/LayoutTests/fast/dom/setCustomValidity-validationMessage-expected.txt b/LayoutTests/fast/dom/setCustomValidity-validationMessage-expected.txt
new file mode 100644
index 0000000000000000000000000000000000000000..31527c0f6fa3d3d0a5a33d6ec06622e284b91a88
--- /dev/null
+++ b/LayoutTests/fast/dom/setCustomValidity-validationMessage-expected.txt
@@ -0,0 +1,49 @@
+Test how setCustomValidity.validationMessage reacts to too few arguments.
+
+On success, you will see a series of "PASS" messages, followed by "TEST COMPLETE".
+
+
+PASS b.setCustomValidity() threw exception TypeError: Failed to execute 'setCustomValidity' on 'HTMLButtonElement': 1 argument required, but only 0 present..
+PASS b.validationMessage is ""
+PASS null is null
+PASS b.validationMessage is ""
+PASS undefined is undefined.
+PASS fs.setCustomValidity() threw exception TypeError: Failed to execute 'setCustomValidity' on 'HTMLFieldSetElement': 1 argument required, but only 0 present..
+PASS fs.validationMessage is ""
+PASS  is undefined.
+PASS fs.validationMessage is ""
+PASS  is undefined.
+PASS i.setCustomValidity() threw exception TypeError: Failed to execute 'setCustomValidity' on 'HTMLInputElement': 1 argument required, but only 0 present..
+PASS i.validationMessage is ""
+PASS null is null
+PASS i.validationMessage is ""
+PASS undefined is undefined.
+PASS k.setCustomValidity() threw exception TypeError: Failed to execute 'setCustomValidity' on 'HTMLKeygenElement': 1 argument required, but only 0 present..
+PASS k.validationMessage is ""
+PASS  is undefined.
+PASS k.validationMessage is ""
+PASS  is undefined.
+PASS ob.setCustomValidity() threw exception TypeError: Failed to execute 'setCustomValidity' on 'HTMLObjectElement': 1 argument required, but only 0 present..
+PASS ob.validationMessage is ""
+PASS  is undefined.
+PASS ob.validationMessage is ""
+PASS  is undefined.
+PASS ou.setCustomValidity() threw exception TypeError: Failed to execute 'setCustomValidity' on 'HTMLOutputElement': 1 argument required, but only 0 present..
+PASS ou.validationMessage is ""
+PASS  is undefined.
+PASS ou.validationMessage is ""
+PASS  is undefined.
+PASS s.setCustomValidity() threw exception TypeError: Failed to execute 'setCustomValidity' on 'HTMLSelectElement': 1 argument required, but only 0 present..
+PASS s.validationMessage is ""
+PASS null is null
+PASS s.validationMessage is ""
+PASS undefined is undefined.
+PASS ta.setCustomValidity() threw exception TypeError: Failed to execute 'setCustomValidity' on 'HTMLTextAreaElement': 1 argument required, but only 0 present..
+PASS ta.validationMessage is ""
+PASS null is null
+PASS ta.validationMessage is ""
+PASS undefined is undefined.
+PASS successfullyParsed is true
+
+TEST COMPLETE
+