LibWeb: Implement Element.hasAttributeNS

Particularly needed by xkcd's Right Click comic. https://xkcd.com/1975/

Userland/Libraries/LibWeb/DOM/Element.cpp

@@ -234,6 +234,17 @@ bool Element::has_attribute(DeprecatedFlyString const& name) const
     return m_attributes->get_attribute(name) != nullptr;
 }
 
+// https://dom.spec.whatwg.org/#dom-element-hasattributens
+bool Element::has_attribute_ns(DeprecatedFlyString namespace_, DeprecatedFlyString const& name) const
+{
+    // 1. If namespace is the empty string, then set it to null.
+    if (namespace_.is_empty())
+        namespace_ = {};
+
+    // 2. Return true if this has an attribute whose namespace is namespace and local name is localName; otherwise false.
+    return m_attributes->get_attribute_ns(namespace_, name) != nullptr;
+}
+
 // https://dom.spec.whatwg.org/#dom-element-toggleattribute
 WebIDL::ExceptionOr<bool> Element::toggle_attribute(DeprecatedFlyString const& name, Optional<bool> force)
 {

Userland/Libraries/LibWeb/DOM/Element.h

@@ -88,6 +88,7 @@ public:
     DeprecatedFlyString const& namespace_uri() const { return namespace_(); }
 
     bool has_attribute(DeprecatedFlyString const& name) const;
+    bool has_attribute_ns(DeprecatedFlyString namespace_, DeprecatedFlyString const& name) const;
     bool has_attributes() const;
     DeprecatedString attribute(DeprecatedFlyString const& name) const { return get_attribute(name); }
     DeprecatedString get_attribute(DeprecatedFlyString const& name) const;

Userland/Libraries/LibWeb/DOM/Element.idl

@@ -35,6 +35,7 @@ interface Element : Node {
     [CEReactions] undefined removeAttribute(DOMString qualifiedName);
     [CEReactions] boolean toggleAttribute(DOMString qualifiedName, optional boolean force);
     boolean hasAttribute(DOMString qualifiedName);
+    boolean hasAttributeNS(DOMString? namespace, DOMString localName);
     boolean hasAttributes();
     [SameObject] readonly attribute NamedNodeMap attributes;
     sequence<DOMString> getAttributeNames();