Add dimension source attribute to HTMLImageElement (#38152)

HTMLImageElement was missing the dimension source attribute, as step 9
from
[here](https://html.spec.whatwg.org/multipage/images.html#updating-the-source-set)
wasn't implemented. This meant that for an element like this:
```html
<picture>
  <source media="(min-width: 1000px)"
    srcset=""
    width="84" height="29">
  <img
    src=""
    width="25" height="25" alt="Wikimedia Foundation" lang="en" loading="lazy">
</picture>
```

The `width` and `height` attributes of the source tag were being
ignored. This broke stuff like these icons on the main page of
Wikipedia.

**Original:**
<img width="2252" height="229" alt="image"
src="https://github.com/user-attachments/assets/fa3fdd9d-5f91-43d4-bc9d-784b0a836d44"
/>


**Fixed:**
<img width="2252" height="229" alt="image"
src="https://github.com/user-attachments/assets/6f4ca4ae-e764-4394-ac31-9a92bbb456ab"
/>


Testing: If there isn't an existing test that covers this I'll make one,
waiting for the github runner to tell me whether this is covered and
then I'll amend the PR

---------

Signed-off-by: Leo Ring <leoring03@gmail.com>
Signed-off-by: Xiaocheng Hu <hu.xiaocheng@huawei.com>
Signed-off-by: Xiaocheng Hu <xiaochengh.work@gmail.com>
Co-authored-by: Xiaocheng Hu <hu.xiaocheng@huawei.com>
Co-authored-by: Xiaocheng Hu <xiaochengh.work@gmail.com>

components/script/dom/htmlimageelement.rs

@@ -162,6 +162,9 @@ pub(crate) struct HTMLImageElement {
     form_owner: MutNullableDom<HTMLFormElement>,
     generation: Cell<u32>,
     source_set: DomRefCell<SourceSet>,
+    /// <https://html.spec.whatwg.org/multipage/#concept-img-dimension-attribute-source>
+    /// Always non-null after construction.
+    dimension_attribute_source: MutNullableDom<Element>,
     last_selected_source: DomRefCell<Option<USVString>>,
     #[ignore_malloc_size_of = "promises are hard"]
     image_decode_promises: DomRefCell<Vec<Rc<Promise>>>,
@@ -737,9 +740,20 @@ impl HTMLImageElement {
             }
 
             // Step 4.9
-            self.normalise_source_densities(&mut source_set, width);
+            if element
+                .get_attribute(&ns!(), &local_name!("width"))
+                .is_some() ||
+                element
+                    .get_attribute(&ns!(), &local_name!("height"))
+                    .is_some()
+            {
+                self.dimension_attribute_source.set(Some(element));
+            }
 
             // Step 4.10
+            self.normalise_source_densities(&mut source_set, width);
+
+            // Step 4.11
             *self.source_set.borrow_mut() = source_set;
             return;
         }
@@ -1348,6 +1362,7 @@ impl HTMLImageElement {
             form_owner: Default::default(),
             generation: Default::default(),
             source_set: DomRefCell::new(SourceSet::new()),
+            dimension_attribute_source: Default::default(),
             last_selected_source: DomRefCell::new(None),
             image_decode_promises: DomRefCell::new(vec![]),
             line_number: creator.return_line_number(),
@@ -1363,14 +1378,18 @@ impl HTMLImageElement {
         creator: ElementCreator,
         can_gc: CanGc,
     ) -> DomRoot<HTMLImageElement> {
-        Node::reflect_node_with_proto(
+        let image_element = Node::reflect_node_with_proto(
             Box::new(HTMLImageElement::new_inherited(
                 local_name, prefix, document, creator,
             )),
             document,
             proto,
             can_gc,
-        )
+        );
+        image_element
+            .dimension_attribute_source
+            .set(Some(image_element.upcast()));
+        image_element
     }
 
     pub(crate) fn areas(&self) -> Option<Vec<DomRoot<HTMLAreaElement>>> {
@@ -1487,6 +1506,16 @@ impl<'dom> LayoutDom<'dom, HTMLImageElement> {
     fn current_request(self) -> &'dom ImageRequest {
         unsafe { self.unsafe_get().current_request.borrow_for_layout() }
     }
+
+    #[allow(unsafe_code)]
+    fn dimension_attribute_source(self) -> LayoutDom<'dom, Element> {
+        unsafe {
+            self.unsafe_get()
+                .dimension_attribute_source
+                .get_inner_as_layout()
+                .expect("dimension attribute source should be always non-null")
+        }
+    }
 }
 
 impl LayoutHTMLImageElementHelpers for LayoutDom<'_, HTMLImageElement> {
@@ -1504,18 +1533,16 @@ impl LayoutHTMLImageElementHelpers for LayoutDom<'_, HTMLImageElement> {
     }
 
     fn get_width(self) -> LengthOrPercentageOrAuto {
-        self.upcast::<Element>()
+        self.dimension_attribute_source()
             .get_attr_for_layout(&ns!(), &local_name!("width"))
-            .map(AttrValue::as_dimension)
+            .map(|x| *AttrValue::from_dimension(x.to_string()).as_dimension())
-            .cloned()
             .unwrap_or(LengthOrPercentageOrAuto::Auto)
     }
 
     fn get_height(self) -> LengthOrPercentageOrAuto {
-        self.upcast::<Element>()
+        self.dimension_attribute_source()
             .get_attr_for_layout(&ns!(), &local_name!("height"))
-            .map(AttrValue::as_dimension)
+            .map(|x| *AttrValue::from_dimension(x.to_string()).as_dimension())
-            .cloned()
             .unwrap_or(LengthOrPercentageOrAuto::Auto)
     }
 }

tests/wpt/meta/html/rendering/replaced-elements/attributes-for-embedded-content-and-images/picture-aspect-ratio.html.ini

@@ -31,9 +31,3 @@
 
   [If we only have height attribute, we should get height mapped but no aspect ratio, even if <img> has attributes.]
     expected: FAIL
-
-  [Loaded picture test: <source> with width and height attributes, <img> without width and height attributes]
-    expected: FAIL
-
-  [Loaded picture test: Both <source> and <img> are with width and height attributes]
-    expected: FAIL