LibWeb: Add CSSStyleSheet.{insert,delete,remove}Rule() APIs

Note that insertRule() is really just a big TODO right now.

Userland/Libraries/LibWeb/CSS/CSSStyleSheet.cpp

@@ -5,6 +5,7 @@
  */
 
 #include <LibWeb/CSS/CSSStyleSheet.h>
+#include <LibWeb/DOM/ExceptionOr.h>
 
 namespace Web::CSS {
 
@@ -17,4 +18,42 @@ CSSStyleSheet::~CSSStyleSheet()
 {
 }
 
+// https://drafts.csswg.org/cssom/#dom-cssstylesheet-insertrule
+DOM::ExceptionOr<unsigned> CSSStyleSheet::insert_rule(StringView rule, unsigned index)
+{
+    // FIXME: 1. If the origin-clean flag is unset, throw a SecurityError exception.
+
+    // FIXME: 2. If the disallow modification flag is set, throw a NotAllowedError DOMException.
+
+    // Let parsed rule be the return value of invoking parse a rule with rule.
+
+    // If parsed rule is a syntax error, return parsed rule.
+
+    // If parsed rule is an @import rule, and the constructed flag is set, throw a SyntaxError DOMException.
+
+    // Return the result of invoking insert a CSS rule rule in the CSS rules at index.
+
+    (void)index;
+    (void)rule;
+    TODO();
+}
+
+// https://drafts.csswg.org/cssom/#dom-cssstylesheet-deleterule
+DOM::ExceptionOr<void> CSSStyleSheet::delete_rule(unsigned index)
+{
+    // FIXME: 1. If the origin-clean flag is unset, throw a SecurityError exception.
+
+    // FIXME: 2. If the disallow modification flag is set, throw a NotAllowedError DOMException.
+
+    // 3. Remove a CSS rule in the CSS rules at index.
+    return m_rules->remove_a_css_rule(index);
+}
+
+// https://drafts.csswg.org/cssom/#dom-cssstylesheet-removerule
+DOM::ExceptionOr<void> CSSStyleSheet::remove_rule(unsigned index)
+{
+    // The removeRule(index) method must run the same steps as deleteRule().
+    return delete_rule(index);
+}
+
 }