Fix for dcall on callable class

tests/language_strong/callable_test.dart

 // Copyright (c) 2012, 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 X {
   call() => 42;
 }
 
 class XX extends X {
   XX.named();
 }
 
 class Y {
   call(int x) => 87 + x;
 
   static int staticMethod(int x) => x + 1;
 }
 
 class Z<T> {
   final T value;
   Z(this.value);
-  call() => value;
+  T call() => value;
 
   static int staticMethod(int x) => x + 1;
 }
 
 typedef F(int x);
 typedef G(String y);
 typedef H();
+typedef T I<T>();
 
 main() {
   X x = new X();
   Function f = x;  // Should pass checked mode test
   Y y = new Y();
   Function g = y;  // Should pass checked mode test
   F f0 = y;  // Should pass checked mode test
   F f1 = x; //# 00: dynamic type error, static type warning
   G g0 = y; //# 01: dynamic type error, static type warning
 
   Expect.equals(f(), 42);
   Expect.equals(g(100), 187);
 
   var z = new Z<int>(123);
   Expect.equals(z(), 123);
-  // TODO(jmesserly): this test doesn't work yet.
-  // Expect.equals((z as dynamic)(), 123);
+  Expect.equals((z as dynamic)(), 123);
 
   Expect.equals(Y.staticMethod(6), 7);
   Expect.equals(Z.staticMethod(6), 7);
 
   var xx = new XX.named();
   Expect.equals(xx(), 42);
 
   H xx2 = new XX.named();
   Expect.equals(xx2(), 42);
 }