wrap_jso should wrap JsArray as well, not always call wrap on its contents

sdk/lib/js/dartium/js_dartium.dart

Index: sdk/lib/js/dartium/js_dartium.dart
diff --git a/sdk/lib/js/dartium/js_dartium.dart b/sdk/lib/js/dartium/js_dartium.dart
index 2e4d9050afd094e2dc80e4f12dfd13ff2f88dfb2..f0e653b123a3555d515adc0cb992963722f077a1 100644
--- a/sdk/lib/js/dartium/js_dartium.dart
+++ b/sdk/lib/js/dartium/js_dartium.dart
@@ -807,11 +807,7 @@ class JsArray<E> extends JsObject with ListMixin<E> {
       _checkIndex(index);
     }
 
-    // Lazily create the Dart class that wraps the JS object when the object in
-    // a list if fetched.
-    var wrap_entry = html.wrap_jso(super[index]);
-    super[index] = wrap_entry;
-    return wrap_entry;
+    return super[index];
   }
 
   void operator []=(index, E value) {