Add a test of the runtime type of a tearoff that uses a covariant generic parameter.

tests/language_2/covariant_tear_off_type_test.dart

Index: tests/language_2/covariant_tear_off_type_test.dart
diff --git a/tests/language_2/covariant_tear_off_type_test.dart b/tests/language_2/covariant_tear_off_type_test.dart
new file mode 100644
index 0000000000000000000000000000000000000000..c3a848c1f0fc13094b4c4773c74e372c2dc80cc1
--- /dev/null
+++ b/tests/language_2/covariant_tear_off_type_test.dart
@@ -0,0 +1,27 @@
+// Copyright (c) 2017, 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";
+
+typedef U F<T, U>(T x);
+
+class C<T> {
+  T f(List<T> x) {}
+}
+
+F<List<num>, num> g(C<num> c) {
+  return c.f;
+}
+
+void main() {
+  var tearoff = g(new C<int>());
+  // Since C.f's x parameter is covariant, its type is changed to Object when
+  // determining the type of the tearoff.  So the type of the tearoff should be
+  // `(Object) -> int`.  (Not, for example, `(List<Object>) -> int` or
+  // `(List<Object>) -> Object`)
+  Expect.isTrue(tearoff is F<Object, int>);
+  // Because the function accepts any object, we can pass strings to it.  This
+  // will not work in Dart 1.
+  Expect.isTrue(tearoff is F<String, int>);
+}