Auto merge of #29711 - switchpiggy:sp3, r=mrobinson

Implemented special cases for Element.clientWidth() and clientHeight()

<!-- Please describe your changes on the following line: -->
Implemented the special cases for Element.clientWidth() and Element.clientHeight() as outlined in issue #29704.

---
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- [x] `./mach build -d` does not report any errors
- [x] `./mach test-tidy` does not report any errors

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- [x] These changes do not require tests because tests already exist.

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[Specification text](https://w3c.github.io/csswg-drafts/cssom-view/#dom-element-clientwidth):
> If the element is the [root element](https://w3c.github.io/csswg-drafts/css-display-4/#root-element) and the element’s [node document](https://dom.spec.whatwg.org/#concept-node-document) is not in [quirks mode](https://dom.spec.whatwg.org/#concept-document-quirks), or if the element is [the body element](https://html.spec.whatwg.org/multipage/dom.html#the-body-element-2) and the element’s node document is in quirks mode, return the [viewport](https://www.w3.org/TR/CSS21/visuren.html#x1) width excluding the size of a rendered scroll bar (if any).

components/script/dom/element.rs

@@ -87,6 +87,7 @@ use crate::task::TaskOnce;
 use devtools_traits::AttrInfo;
 use dom_struct::dom_struct;
 use euclid::default::Rect;
+use euclid::default::Size2D;
 use html5ever::serialize;
 use html5ever::serialize::SerializeOpts;
 use html5ever::serialize::TraversalScope;
@@ -3292,7 +3293,25 @@ impl Element {
         {
             return rect;
         }
-        let rect = self.upcast::<Node>().client_rect();
+
+        let mut rect = self.upcast::<Node>().client_rect();
+        let in_quirks_mode = self.node.owner_doc().quirks_mode() == QuirksMode::Quirks;
+
+        if (in_quirks_mode &&
+            self.node.owner_doc().GetBody().as_deref() == self.downcast::<HTMLElement>()) ||
+            (!in_quirks_mode && *self.root_element() == *self)
+        {
+            let viewport_dimensions = self
+                .node
+                .owner_doc()
+                .window()
+                .window_size()
+                .initial_viewport
+                .round()
+                .to_i32();
+            rect.size = Size2D::<i32>::new(viewport_dimensions.width, viewport_dimensions.height);
+        }
+
         self.ensure_rare_data().client_rect = Some(window_from_node(self).cache_layout_value(rect));
         rect
     }

tests/wpt/metadata-layout-2020/css/cssom-view/client-props-root.html.ini

@@ -1,4 +0,0 @@
-[client-props-root.html]
-  [client* properties on the root element]
-    expected: FAIL
-

tests/wpt/metadata-layout-2020/css/cssom-view/scrolling-quirks-vs-nonquirks.html.ini

@@ -2,9 +2,6 @@
   [scrollingElement in non-quirks mode]
     expected: FAIL
 
-  [clientWidth/clientHeight on the HTML body element in quirks mode]
-    expected: FAIL
-
   [scrollLeft/scrollRight of the content in quirks mode]
     expected: FAIL
 
@@ -14,9 +11,6 @@
   [scrollingElement in quirks mode]
     expected: FAIL
 
-  [clientWidth/clientHeight on the root element in non-quirks mode]
-    expected: FAIL
-
   [scrollWidth/scrollHeight on the root element in quirks mode]
     expected: FAIL
 

tests/wpt/metadata/css/cssom-view/client-props-root.html.ini

@@ -1,4 +0,0 @@
-[client-props-root.html]
-  [client* properties on the root element]
-    expected: FAIL
-

tests/wpt/metadata/css/cssom-view/scrolling-quirks-vs-nonquirks.html.ini

@@ -8,9 +8,6 @@
   [scrollWidth/scrollHeight on the HTML body element in quirks mode]
     expected: FAIL
 
-  [clientWidth/clientHeight on the HTML body element in quirks mode]
-    expected: FAIL
-
   [scrollLeft/scrollRight of the content in quirks mode]
     expected: FAIL
 
@@ -20,9 +17,6 @@
   [scrollWidth/scrollHeight on the root element in non-quirks mode]
     expected: FAIL
 
-  [clientWidth/clientHeight on the root element in non-quirks mode]
-    expected: FAIL
-
   [scroll() on the HTML body element in non-quirks mode]
     expected: FAIL