LibWeb: Add specialized fast_is for lists

Before:
  `is<HTMLOLListElement>` and other similar calls in this commit
  are resolved to `dynamic_cast`, which incurs runtime overhead
  for resolving the type. The Performance hit becomes apparent
  when rendering large lists. Callgrind analysis points to a
  significant performance hit from calls to `is<...>` in
  `Element::list_owner`.

Reference: Michael Gibbs and Bjarne Stroustrup (2006) Fast dynamic
casting. Softw. Pract. Exper. 2006; 36:139–156

After:
  Implement inline `fast_is` virtual method that immediately
  resolves the type. Results in noticeable performance improvement
  2x-ish for lists with 20K entries.

Bonus: Convert starting value for LI elements to signed integer
    The spec requires the start attribute and starting value to be
    "integer". Firefox and Chrome support a negative start attribute.

FIXME: At the time of this PR, about 134 other objects resolve
`is<...>` to `dynamic_cast`. It may be a good idea to coordinate
similar changes to at least [some of] the ones that my have impact
on performance (maybe open a new issue?).

Libraries/LibWeb/HTML/HTMLLIElement.h

@@ -41,6 +41,8 @@ public:
         MUST(set_attribute(AttributeNames::value, String::number(value)));
     }
 
+    virtual bool is_html_li_element() const override { return true; }
+
 private:
     HTMLLIElement(DOM::Document&, DOM::QualifiedName);
 
@@ -52,3 +54,10 @@ private:
 };
 
 }
+
+namespace Web::DOM {
+
+template<>
+inline bool Node::fast_is<Web::HTML::HTMLLIElement>() const { return is_html_li_element(); }
+
+}

Libraries/LibWeb/HTML/HTMLMenuElement.h

@@ -21,6 +21,8 @@ public:
     // https://www.w3.org/TR/html-aria/#el-menu
     virtual Optional<ARIA::Role> default_role() const override { return ARIA::Role::list; }
 
+    virtual bool is_html_menu_element() const override { return true; }
+
 private:
     HTMLMenuElement(DOM::Document&, DOM::QualifiedName);
 
@@ -28,3 +30,10 @@ private:
 };
 
 }
+
+namespace Web::DOM {
+
+template<>
+inline bool Node::fast_is<Web::HTML::HTMLMenuElement>() const { return is_html_menu_element(); }
+
+}

Libraries/LibWeb/HTML/HTMLOListElement.cpp

@@ -11,6 +11,7 @@
 #include <LibWeb/HTML/AttributeNames.h>
 #include <LibWeb/HTML/HTMLOListElement.h>
 #include <LibWeb/HTML/Numbers.h>
+#include <LibWeb/WebIDL/Types.h>
 
 namespace Web::HTML {
 
@@ -49,7 +50,7 @@ WebIDL::Long HTMLOListElement::start()
 }
 
 // https://html.spec.whatwg.org/multipage/grouping-content.html#concept-ol-start
-size_t HTMLOListElement::starting_value() const
+AK::Checked<i32> HTMLOListElement::starting_value() const
 {
     // 1. If the ol element has a start attribute, then:
     auto start = get_attribute(AttributeNames::start);
@@ -61,10 +62,11 @@ size_t HTMLOListElement::starting_value() const
         if (parsed.has_value())
             return parsed.value();
     }
-
     // 2. If the ol element has a reversed attribute, then return the number of owned li elements.
     if (has_attribute(AttributeNames::reversed)) {
-        return number_of_owned_list_items();
+        auto const reverse_list_starting_value = number_of_owned_list_items();
+        VERIFY(reverse_list_starting_value <= NumericLimits<WebIDL::Long>::max());
+        return reverse_list_starting_value;
     }
 
     // 3. Return 1.

Libraries/LibWeb/HTML/HTMLOListElement.h

@@ -6,6 +6,7 @@
 
 #pragma once
 
+#include <AK/Checked.h>
 #include <LibWeb/ARIA/Roles.h>
 #include <LibWeb/HTML/HTMLElement.h>
 #include <LibWeb/WebIDL/Types.h>
@@ -28,7 +29,9 @@ public:
         MUST(set_attribute(AttributeNames::start, String::number(start)));
     }
 
-    size_t starting_value() const;
+    AK::Checked<i32> starting_value() const;
+
+    virtual bool is_html_olist_element() const override { return true; }
 
 private:
     HTMLOListElement(DOM::Document&, DOM::QualifiedName);
@@ -41,3 +44,10 @@ private:
 };
 
 }
+
+namespace Web::DOM {
+
+template<>
+inline bool Node::fast_is<Web::HTML::HTMLOListElement>() const { return is_html_olist_element(); }
+
+}

Libraries/LibWeb/HTML/HTMLUListElement.h

@@ -21,6 +21,8 @@ public:
     // https://www.w3.org/TR/html-aria/#el-ul
     virtual Optional<ARIA::Role> default_role() const override { return ARIA::Role::list; }
 
+    virtual bool is_html_ulist_element() const override { return true; }
+
 private:
     HTMLUListElement(DOM::Document&, DOM::QualifiedName);
 
@@ -31,3 +33,10 @@ private:
 };
 
 }
+
+namespace Web::DOM {
+
+template<>
+inline bool Node::fast_is<Web::HTML::HTMLUListElement>() const { return is_html_ulist_element(); }
+
+}