MutableVariable no longer has a host Element.

tests/compiler/dart2js/backend_dart/sexpr_unstringifier.dart

Index: tests/compiler/dart2js/backend_dart/sexpr_unstringifier.dart
diff --git a/tests/compiler/dart2js/backend_dart/sexpr_unstringifier.dart b/tests/compiler/dart2js/backend_dart/sexpr_unstringifier.dart
index a55437e7dd2062212e8c4394105edf944ff90852..2c8ff499e89ba8fe5003e8277265e7d9f3aaaba2 100644
--- a/tests/compiler/dart2js/backend_dart/sexpr_unstringifier.dart
+++ b/tests/compiler/dart2js/backend_dart/sexpr_unstringifier.dart
@@ -712,8 +712,7 @@ class SExpressionUnstringifier {
 
   MutableVariable addMutableVariable(String name) {
     assert(!name2variable.containsKey(name));
-    MutableVariable variable =
-        new MutableVariable(new DummyElement(""), new DummyElement(name));
+    MutableVariable variable = new MutableVariable(new DummyElement(name));
     name2variable[name] = variable;
     return variable;
   }