dart2js: set effective target for patched constructors

tests/compiler/dart2js/patch_test.dart

Index: tests/compiler/dart2js/patch_test.dart
diff --git a/tests/compiler/dart2js/patch_test.dart b/tests/compiler/dart2js/patch_test.dart
index 1422a1a3958d8edb5b823c0315f1db07050ad87d..660a803502a3dca97dcd49ac9d52c456a7fcb06a 100644
--- a/tests/compiler/dart2js/patch_test.dart
+++ b/tests/compiler/dart2js/patch_test.dart
@@ -953,7 +953,9 @@ Future testEffectiveTarget() async {
     """;
   String patch = """
     @patch class B {
+      @patch
       B.patchTarget() : super();
+      @patch
       factory B.reflectBack() = B.originTarget;
     }
     """;
@@ -1025,7 +1027,7 @@ main() {
 
     await testPatchAndSelector();
 
-    await testEffectiveTarget(); /// bug: ok
+    await testEffectiveTarget();
 
     await testAnalyzeAllInjectedMembers();
     await testTypecheckPatchedMembers();