Fix dispatch name of covariance-checked calls.

tests/language_strong/covariant_subtyping_unsafe_call1_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 Foo<T> {
+  method(T x) {}
+}
+
+main() {
+  Foo<int> intFoo = new Foo<int>();
+  Foo<num> numFoo = intFoo;
+  Expect.throws(() => numFoo.method(2.5));
+}