Switched `Element.renderObject` to iterative implementation. (#112885)

packages/flutter/lib/src/widgets/framework.dart

@@ -3418,19 +3418,22 @@ abstract class Element extends DiagnosticableTree implements BuildContext {
   /// this location in the tree. Otherwise, this getter will walk down the tree
   /// until it finds a [RenderObjectElement].
   RenderObject? get renderObject {
-    RenderObject? result;
-    void visit(Element element) {
-      assert(result == null); // this verifies that there's only one child
-      if (element._lifecycleState == _ElementLifecycle.defunct) {
-        return;
-      } else if (element is RenderObjectElement) {
-        result = element.renderObject;
+    Element? current = this;
+    while (current != null) {
+      if (current._lifecycleState == _ElementLifecycle.defunct) {
+        break;
+      } else if (current is RenderObjectElement) {
+        return current.renderObject;
       } else {
-        element.visitChildren(visit);
+        Element? next;
+        current.visitChildren((Element child) {
+          assert(next == null);  // This verifies that there's only one child.
+          next = child;
+        });
+        current = next;
       }
     }
-    visit(this);
-    return result;
+    return null;
   }
 
   @override