Use null type argument vector instead of vector of Dynamic for a generic raw

tests/language/src/GenericInstanceof2Test.dart

+// Copyright (c) 2012, 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.
+// Test that instanceof works correctly with type variables.
+
+// Test that partially typed generic instances are correctly constructed.
+
+// Test factory case.
+class Foo<K, V> {
+  Foo() { }
+
+  factory Foo.fac() {
+    return new Foo<K, V>();
+  }
+
+  FooString() {
+    return new Foo<K, String>.fac();
+  }
+}
+
+// Test constructor case.
+class Moo<K, V> {
+  Moo() { }
+
+  MooString() {
+    return new Moo<K, String>();
+  }
+}
+
+main () {
+  var foo_int_num = new Foo<int, num>();
+  Expect.isTrue(foo_int_num is Foo<int, num>);
+  Expect.isTrue(foo_int_num is !Foo<int, String>);
+  // foo_int_num.FooString() returns a Foo<int, String>
+  Expect.isTrue(foo_int_num.FooString() is !Foo<int, num>);
+  Expect.isTrue(foo_int_num.FooString() is Foo<int, String>);
+
+  var foo_raw = new Foo();
+  Expect.isTrue(foo_raw is Foo<int, num>);
+  Expect.isTrue(foo_raw is Foo<int, String>);
+  // foo_raw.FooString() returns a Foo<Dynamic, String>
+  Expect.isTrue(foo_raw.FooString() is !Foo<int, num>);
+  Expect.isTrue(foo_raw.FooString() is Foo<int, String>);
+
+  var moo_int_num = new Moo<int, num>();
+  Expect.isTrue(moo_int_num is Moo<int, num>);
+  Expect.isTrue(moo_int_num is !Moo<int, String>);
+  // moo_int_num.MooString() returns a Moo<int, String>
+  Expect.isTrue(moo_int_num.MooString() is !Moo<int, num>);
+  Expect.isTrue(moo_int_num.MooString() is Moo<int, String>);
+
+  var moo_raw = new Moo();
+  Expect.isTrue(moo_raw is Moo<int, num>);
+  Expect.isTrue(moo_raw is Moo<int, String>);
+  // moo_raw.MooString() returns a Moo<Dynamic, String>
+  Expect.isTrue(moo_raw.MooString() is !Moo<int, num>);
+  Expect.isTrue(moo_raw.MooString() is Moo<int, String>);
+}