Fix dispatch name of covariance-checked calls.

tests/language_strong/covariant_subtyping_unsafe_call2_test.dart

+// Copyright (c) 2016, the Dart project authors.  Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+import 'package:expect/expect.dart';
+
+class Implementation {
+  method(int x) {}
+}
+
+abstract class Interface<T> {
+  method(T x);
+}
+
+class Subclass extends Implementation implements Interface<int> {}
+
+main() {
+  Subclass subclass = new Subclass();
+  Interface<int> intInterface = subclass;
+  Interface<num> numInterface = intInterface;
+  Expect.throws(() => numInterface.method(2.5));
+}