Support runtime check of function types.

tests/compiler/dart2js/subtype_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.
 
 library subtype_test;
 
 import 'package:expect/expect.dart';
 import 'type_test_helper.dart';
 import '../../../sdk/lib/_internal/compiler/implementation/dart_types.dart';
 import "../../../sdk/lib/_internal/compiler/implementation/elements/elements.dart"
@@ skipping 246 matching lines @@
   expect(true, A, function);
   expect(true, A, m1);
   expect(true, A, m2);
   expect(false, A, m3);
   expect(false, A, m4);
   expect(true, A, m5);
 }
 
 testFunctionSubtyping() {
   var env = new TypeEnvironment(r"""
+      _() => null;
       void void_() {}
       void void_2() {}
       int int_() => 0;
       int int_2() => 0;
       Object Object_() => null;
       double double_() => 0.0;
       void void__int(int i) {}
       int int__int(int i) => 0;
       int int__int2(int i) => 0;
       int int__Object(Object o) => 0;
       Object Object__int(int i) => null;
       int int__double(double d) => 0;
       int int__int_int(int i1, int i2) => 0;
       void inline_void_(void f()) {}
       void inline_void__int(void f(int i)) {}
       """);
   functionSubtypingHelper(env);
 }
 
 testTypedefSubtyping() {
   var env = new TypeEnvironment(r"""
+      typedef _();
       typedef void void_();
       typedef void void_2();
       typedef int int_();
       typedef int int_2();
       typedef Object Object_();
       typedef double double_();
       typedef void void__int(int i);
       typedef int int__int(int i);
       typedef int int__int2(int i);
       typedef int int__Object(Object o);
@@ skipping 12 matching lines @@
     DartType supertype = env.getElementType(sup);
     Expect.equals(expectedResult, env.isSubtype(subtype, supertype),
         '$subtype <: $supertype');
   }
 
   // () -> int <: Function
   expect(true, 'int_', 'Function');
   // Function <: () -> int
   expect(false, 'Function', 'int_');
 
+  // () -> dynamic <: () -> dynamic
+  expect(true, '_', '_');
+  // () -> dynamic <: () -> void
+  expect(true, '_', 'void_');
+  // () -> void <: () -> dynamic
+  expect(true, 'void_', '_');
+
   // () -> int <: () -> void
   expect(true, 'int_', 'void_');
   // () -> void <: () -> int
   expect(false, 'void_', 'int_');
   // () -> void <: () -> void
   expect(true, 'void_', 'void_2');
   // () -> int <: () -> int
   expect(true, 'int_', 'int_2');
   // () -> int <: () -> Object
   expect(true, 'int_', 'Object_');
@@ skipping 390 matching lines @@
   expect(true, J_U, Object_);
   expect(false, J_U, num_);
   expect(false, J_U, int_);
   expect(false, J_U, String_);
   expect(true, J_U, dynamic_);
   expect(false, J_U, J_T);
   expect(true, J_U, J_S);
   expect(true, J_U, J_U);
   expect(false, J_U, A_T);
 }