dart2js cps: Support function types in 'is' and 'as' operators.

tests/language/function_subtype3_test.dart

+// Copyright (c) 2015, 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';
+
+class FunctionLike<T> {
+  call(T arg) {
+    return arg;
+  }
+}
+
+class Foo<T> {
+  testString() => new FunctionLike<String>() is T;
+  testInt() => new FunctionLike<int>() is T;
+}
+
+typedef TakeString(String arg);
+typedef TakeInt(int arg);
+
+main() {
+  Foo<TakeString> stringFoo = new Foo<TakeString>();
+  Foo<TakeInt> intFoo = new Foo<TakeInt>();
+
+  Expect.isTrue(stringFoo.testString());
+  Expect.isFalse(stringFoo.testInt());
+
+  Expect.isFalse(intFoo.testString());
+  Expect.isTrue(intFoo.testInt());
+}