LibWeb: Make StyleSheetList.item an IDL getter

Meta/Lagom/Tools/CodeGenerators/LibWeb/WrapperGenerator.cpp

@@ -1460,6 +1460,7 @@ void generate_implementation(IDL::Interface const& interface)
 #include <LibJS/Runtime/Value.h>
 #include <LibWeb/Bindings/@prototype_class@.h>
 #include <LibWeb/Bindings/@wrapper_class@.h>
+#include <LibWeb/Bindings/CSSStyleSheetWrapper.h>
 #include <LibWeb/Bindings/CanvasRenderingContext2DWrapper.h>
 #include <LibWeb/Bindings/CommentWrapper.h>
 #include <LibWeb/Bindings/DOMImplementationWrapper.h>

Userland/Libraries/LibWeb/CSS/StyleSheetList.cpp

@@ -18,4 +18,15 @@ StyleSheetList::StyleSheetList(DOM::Document& document)
 {
 }
 
+// https://drafts.csswg.org/cssom/#ref-for-dfn-supported-property-indices%E2%91%A1
+bool StyleSheetList::is_supported_property_index(u32 index) const
+{
+    // The object’s supported property indices are the numbers in the range zero to one less than the number of CSS style sheets represented by the collection.
+    // If there are no such CSS style sheets, then there are no supported property indices.
+    if (m_sheets.is_empty())
+        return false;
+
+    return index < m_sheets.size();
+}
+
 }

Userland/Libraries/LibWeb/CSS/StyleSheetList.h

@@ -37,6 +37,8 @@ public:
 
     size_t length() const { return m_sheets.size(); }
 
+    bool is_supported_property_index(u32) const;
+
 private:
     explicit StyleSheetList(DOM::Document&);
 

Userland/Libraries/LibWeb/CSS/StyleSheetList.idl

@@ -1,5 +1,5 @@
+[Exposed=Window]
 interface StyleSheetList {
-    // FIXME: item() should be a WebIDL "getter"
-    CSSStyleSheet? item(unsigned long index);
+    getter CSSStyleSheet? item(unsigned long index);
     readonly attribute unsigned long length;
 };