Use closure tracer to identify closures that are not passed to Function.apply

tests/compiler/dart2js/map_tracer_const_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.
+
+import 'package:expect/expect.dart';
+import "package:async_helper/async_helper.dart";
+
+import 'compiler_helper.dart';
+import 'type_mask_test_helper.dart';
+
+const String TEST = '''
+int closure(int x) {
+  return x;
+}
+
+class A {
+  static const DEFAULT = const {'fun' : closure};
+
+  final map;
+
+  A([maparg]) : map = maparg == null ? DEFAULT : maparg;
+}
+
+main() {
+  var a = new A();
+  a.map['fun'](3.3);
+  print(closure(22));
+}
+''';
+
+void main() {
+  Uri uri = new Uri(scheme: 'source');
+  var compiler = compilerFor(TEST, uri,
+      expectedErrors: 0, expectedWarnings: 0);
+  compiler.stopAfterTypeInference = true;
+  asyncTest(() => compiler.runCompiler(uri).then((_) {
+    var typesTask = compiler.typesTask;
+    var typesInferrer = typesTask.typesInferrer;
+    var element = findElement(compiler, 'closure');
+    var mask = typesInferrer.getReturnTypeOfElement(element);
+    Expect.equals(typesTask.numType, simplify(mask, compiler));
+  }));
+}