Fix inferrer test by forcing instantiation of a closure.

tests/compiler/dart2js/simple_inferrer_test.dart

 // Copyright (c) 2013, 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';
 import
     '../../../sdk/lib/_internal/compiler/implementation/types/types.dart'
     show TypeMask;
 
 import 'compiler_helper.dart';
@@ skipping 368 matching lines @@
   returnInt3() => ++new A()[0];
   returnInt4() => new A()[0] += 42;
   returnInt5() => ++super.myField;
   returnInt6() => super.myField += 4;
   returnInt7() => ++super[0];
   returnInt8() => super[0] += 54;
   returnInt9() => super.myField;
 }
 
 main() {
+  // Ensure a function class is being instantiated.
+  () => 42;
   returnNum1(true);
   returnNum2(true);
   returnInt1(true);
   returnInt2(true);
   returnInt3(true);
   returnInt4();
   returnDouble(true);
   returnGiveUp(true);
   returnInt5();
   returnInt6();
@@ skipping 153 matching lines @@
   checkReturnInClass('B', 'returnInt9', typesInferrer.intType);
 
   checkFactoryConstructor(String className) {
     var cls = findElement(compiler, className);
     var element = cls.localLookup(buildSourceString(className));
     Expect.equals(new TypeMask.nonNullExact(cls.rawType),
                   typesInferrer.internal.returnTypeOf[element]);
   }
   checkFactoryConstructor('A');
 }