servo: Merge #12911 - stylo: Traverse anonymous children when styling (from bholley:traverse_anonymous_children); r=emilio

The corresponding Gecko changes are at https://bugzilla.mozilla.org/show_bug.cgi?id=1292662

Source-Repo: https://github.com/servo/servo
Source-Revision: 8e39313321791cade116b3a5f34a36d8cf99c0f2

servo/components/script/layout_wrapper.rs

@@ -115,6 +115,7 @@ impl<'ln> TNode for ServoLayoutNode<'ln> {
     type ConcreteElement = ServoLayoutElement<'ln>;
     type ConcreteDocument = ServoLayoutDocument<'ln>;
     type ConcreteRestyleDamage = RestyleDamage;
+    type ConcreteChildrenIterator = ServoChildrenIterator<'ln>;
 
     fn to_unsafe(&self) -> UnsafeNode {
         unsafe {
@@ -147,6 +148,12 @@ impl<'ln> TNode for ServoLayoutNode<'ln> {
         self.dump_style_indent(0);
     }
 
+    fn children(self) -> ServoChildrenIterator<'ln> {
+        ServoChildrenIterator {
+            current: self.first_child(),
+        }
+    }
+
     fn opaque(&self) -> OpaqueNode {
         unsafe { self.get_jsmanaged().opaque() }
     }
@@ -163,10 +170,6 @@ impl<'ln> TNode for ServoLayoutNode<'ln> {
         self.opaque().0
     }
 
-    fn children_count(&self) -> u32 {
-        unsafe { self.node.children_count() }
-    }
-
     fn as_element(&self) -> Option<ServoLayoutElement<'ln>> {
         as_element(self.node)
     }
@@ -280,6 +283,19 @@ impl<'ln> TNode for ServoLayoutNode<'ln> {
     }
 }
 
+pub struct ServoChildrenIterator<'a> {
+    current: Option<ServoLayoutNode<'a>>,
+}
+
+impl<'a> Iterator for ServoChildrenIterator<'a> {
+    type Item = ServoLayoutNode<'a>;
+    fn next(&mut self) -> Option<ServoLayoutNode<'a>> {
+        let node = self.current;
+        self.current = node.and_then(|node| node.next_sibling());
+        node
+    }
+}
+
 impl<'ln> LayoutNode for ServoLayoutNode<'ln> {
     type ConcreteThreadSafeLayoutNode = ServoThreadSafeLayoutNode<'ln>;