Remove other occurencies of _unwrap from dart:html.

lib/dom/src/native_DOMPublic.dart

Index: lib/dom/src/native_DOMPublic.dart
diff --git a/lib/dom/src/native_DOMPublic.dart b/lib/dom/src/native_DOMPublic.dart
index dba636bef4ef0c50acba5ef6e4e5357169270e7f..fe76bea11d339f31e90d2ea4029d45bca0f21a49 100644
--- a/lib/dom/src/native_DOMPublic.dart
+++ b/lib/dom/src/native_DOMPublic.dart
@@ -3,8 +3,7 @@
 // BSD-style license that can be found in the LICENSE file.
 
 // This API is exploratory.
-spawnDomIsolate(Window targetWindowWrapped, String entryPoint) {
-  final targetWindow = _unwrap(targetWindowWrapped);
+spawnDomIsolate(Window targetWindow, String entryPoint) {
   if (targetWindow is! _DOMWindowImpl && targetWindow is! _DOMWindowCrossFrameImpl) {
     throw 'Bad window argument: $targetWindow';
   }