LibWeb: Implement document.anchors

This returns an HTMLCollection of all <a> elements in the document that
have a "name" attribute.

Userland/Libraries/LibWeb/DOM/Document.cpp

@@ -32,6 +32,7 @@
 #include <LibWeb/Dump.h>
 #include <LibWeb/HTML/AttributeNames.h>
 #include <LibWeb/HTML/EventNames.h>
+#include <LibWeb/HTML/HTMLAnchorElement.h>
 #include <LibWeb/HTML/HTMLBodyElement.h>
 #include <LibWeb/HTML/HTMLFrameSetElement.h>
 #include <LibWeb/HTML/HTMLHeadElement.h>
@@ -517,6 +518,15 @@ NonnullRefPtr<HTMLCollection> Document::applets()
     return HTMLCollection::create(*this, [] { return false; });
 }
 
+NonnullRefPtr<HTMLCollection> Document::anchors()
+{
+    // FIXME: This should return the same HTMLCollection object every time,
+    //        but that would cause a reference cycle since HTMLCollection refs the root.
+    return HTMLCollection::create(*this, [](Element const& element) {
+        return is<HTML::HTMLAnchorElement>(element) && element.has_attribute(HTML::AttributeNames::name);
+    });
+}
+
 Color Document::link_color() const
 {
     if (m_link_color.has_value())

Userland/Libraries/LibWeb/DOM/Document.h

@@ -141,6 +141,7 @@ public:
     NonnullRefPtr<HTMLCollection> get_elements_by_class_name(FlyString const&);
 
     NonnullRefPtr<HTMLCollection> applets();
+    NonnullRefPtr<HTMLCollection> anchors();
 
     const String& source() const { return m_source; }
     void set_source(const String& source) { m_source = source; }

Userland/Libraries/LibWeb/DOM/Document.idl

@@ -19,6 +19,7 @@ interface Document : Node {
     HTMLCollection getElementsByClassName(DOMString className);
 
     readonly attribute HTMLCollection applets;
+    readonly attribute HTMLCollection anchors;
 
     Element createElement(DOMString tagName);
     Element createElementNS(DOMString? namespace, DOMString qualifiedName);