Bug 1258205 - Make setAttribute throw InvalidCharacterError if the attribute already exists. r=baku

dom/base/Element.cpp

@@ -1177,14 +1177,12 @@ Element::SetAttribute(const nsAString& aName,
                       const nsAString& aValue,
                       ErrorResult& aError)
 {
+  aError = nsContentUtils::CheckQName(aName, false);
+  if (aError.Failed()) {
+    return;
+  }
   const nsAttrName* name = InternalGetExistingAttrNameFromQName(aName);
-
   if (!name) {
-    aError = nsContentUtils::CheckQName(aName, false);
-    if (aError.Failed()) {
-      return;
-    }
-
     nsCOMPtr<nsIAtom> nameAtom;
     if (IsHTMLElement() && IsInHTMLDocument()) {
       nsAutoString lower;

testing/web-platform/meta/dom/nodes/attributes.html.ini

@@ -6,6 +6,3 @@
   [First set attribute is returned with mapped attribute set first]
     expected: FAIL
 
-  [When qualifiedName does not match the Name production, an INVALID_CHARACTER_ERR exception is to be thrown, even if the attribute is already present. (setAttribute)]
-    expected: FAIL
-