classes with call-methods were not recognized as Functions.

tests/language/function_propagation_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";
+
+class A {
+  int call(String str) => 499;
+}
+
+typedef int F(String str);
+
+main() {
+  var a = new A();
+  if (a is Function) {
+    Expect.isTrue(a is A);
+  } else {
+    Expect.fail("a should be a Function");
+  }
+
+  var a2 = new A();
+  if (a2 is F) {
+    Expect.isTrue(a2 is A);
+  } else {
+    Expect.fail("a2 should be an F");
+  }
+
+  Function a3 = new A();
+  // Dart2Js mistakenly assumed that Function and A couldn't be related and
+  // returned false for a is A.
+  Expect.isTrue(a3 is A);
+
+  F a4 = new A();
+  Expect.isTrue(a4 is A);
+}