LibWeb/HTML: Implement HTMLImageElement::allows_auto_sizes()

Author: https://github.com/AtkinsSJ
Commit: 99718653e2
Pull-request: https://github.com/LadybirdBrowser/ladybird/pull/1374

Userland/Libraries/LibWeb/HTML/HTMLImageElement.cpp

@@ -1171,4 +1171,17 @@ void HTMLImageElement::set_decoding(String decoding)
         m_decoding_hint = ImageDecodingHint::Auto;
 }
 
+bool HTMLImageElement::allows_auto_sizes() const
+{
+    // An img element allows auto-sizes if:
+    // - its loading attribute is in the Lazy state, and
+    // - its sizes attribute's value is "auto" (ASCII case-insensitive), or starts with "auto," (ASCII case-insensitive).
+    if (lazy_loading_attribute() != LazyLoading::Lazy)
+        return false;
+    auto sizes = attribute(HTML::AttributeNames::sizes);
+    return sizes.has_value()
+        && (sizes->equals_ignoring_ascii_case("auto"sv)
+            || sizes->starts_with_bytes("auto,"sv, AK::CaseSensitivity::CaseInsensitive));
+}
+
 }

Userland/Libraries/LibWeb/HTML/HTMLImageElement.h

@@ -94,6 +94,9 @@ public:
     // https://html.spec.whatwg.org/multipage/images.html#upgrade-the-pending-request-to-the-current-request
     void upgrade_pending_request_to_current_request();
 
+    // https://html.spec.whatwg.org/multipage/embedded-content.html#allows-auto-sizes
+    bool allows_auto_sizes() const;
+
     // ^Layout::ImageProvider
     virtual bool is_image_available() const override;
     virtual Optional<CSSPixels> intrinsic_width() const override;