Always treat [call] members as closures during tracing.

tests/compiler/dart2js_extra/18383_test.dart

 // Copyright (c) 2014, 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.
 
-// Tests that typechecks on const objects with typedefs work.
+// Regression test for http://dartbug.com/18383
 
 import "package:expect/expect.dart";
 
-typedef String Int2String(int x);
-
-class A {
-  final Int2String f;
-  const A(this.f);
+class F {
+  call() => (x) => new G(x.toInt());
 }
 
-String foo(int x) => "str";
-
-const a = const A(foo);
+class G {
+  var z;
+  G(this.z);
+  foo() => '$this.foo';
+  toString() => 'G($z)';
+}
 
 main() {
-  Expect.equals("str", a.f(499));
+  var f = new F();
+  var m = f();
+  Expect.equals(m(66).foo(), "G(66).foo");
 }
+