Make 'mode' required parameter for Element.attachShadow

third_party/WebKit/LayoutTests/imported/web-platform-tests/shadow-dom/Element-interface-attachShadow-expected.txt

Index: third_party/WebKit/LayoutTests/imported/web-platform-tests/shadow-dom/Element-interface-attachShadow-expected.txt
diff --git a/third_party/WebKit/LayoutTests/imported/web-platform-tests/shadow-dom/Element-interface-attachShadow-expected.txt b/third_party/WebKit/LayoutTests/imported/web-platform-tests/shadow-dom/Element-interface-attachShadow-expected.txt
index 47dee12c09a786eb82b9aa7fb36c5f00152b12da..9eb1da079a8d0395bcd936fb083faf562402f846 100644
--- a/third_party/WebKit/LayoutTests/imported/web-platform-tests/shadow-dom/Element-interface-attachShadow-expected.txt
+++ b/third_party/WebKit/LayoutTests/imported/web-platform-tests/shadow-dom/Element-interface-attachShadow-expected.txt
@@ -1,8 +1,7 @@
 This is a testharness.js-based test.
 PASS Check the existence of Element.attachShadow 
 PASS Nodes other than Element should not have attachShadow 
-FAIL Element.attachShadow must throw a TypeError if mode is not "open" or "closed" assert_throws: attachShadow must throw a TypeError when mode is omitted function "function () {
-        document.createElement('div').attac..." did not throw
+PASS Element.attachShadow must throw a TypeError if mode is not "open" or "closed" 
 PASS Element.attachShadow must create an instance of ShadowRoot 
 PASS Element.attachShadow must throw a InvalidStateError if the context object already hosts a shadow tree 
 FAIL Element.attachShadow must throw a NotSupportedError for button, details, input, marquee, meter, progress, select, textarea, and keygen elements assert_throws: Calling attachShadow({mode: "open"}) on button element must throw function "function () {