Support synthetic default constructors.

tests/compiler/dart2js/js_backend_cps_ir_basic.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 for basic functionality.
 
 library basic_tests;
 
 import 'js_backend_cps_ir_test.dart';
 
@@ skipping 67 matching lines @@
   const TestEntry("""
 main() {
   print(new Set());
   print(new Set.from([1, 2, 3]));
 }""", r"""
 function() {
   P.print(P.Set_Set());
   P.print(P.Set_Set$from([1, 2, 3]));
   return null;
 }"""),
+  // Call synthetic constructor.
+  const TestEntry("""
+class C {}
+main() {
+  print(new C());
+}"""),
   // Method invocation
   const TestEntry("""
 main() {
   print(new DateTime.now().isBefore(new DateTime.now()));
 }""", r"""
 function() {
   P.print(P.DateTime$now().isBefore$1(P.DateTime$now()));
   return null;
 }"""),
 ];