Complete support for type variables in new expressions.

tests/language/generic_creation_test.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.
+
+class A<X, Y, Z> {
+  shift() => new A<Z, X, Y>();
+  swap() => new A<Z, Y, X>();
+  first() => new A<X, X, X>();
+  last() => new A<Z, Z, Z>();
+  wrap() => new A<A<X, X, X>, A<Y, Y, Y>, A<Z, Z, Z>>();
+}
+
+class U {}
+class V {}
+class W {}
+
+sameType(a, b) => Expect.identical(a.runtimeType, b.runtimeType);
+
+main() {
+  A a = new A<U, V, W>();
+  sameType(new A<W, U, V>(), a.shift());
+  sameType(new A<W, V, U>(), a.swap());
+  sameType(new A<U, U, U>(), a.first());
+  sameType(new A<W, W, W>(), a.last());
+  sameType(new A<A<U, U, U>, A<V, V, V>, A<W, W, W>>(), a.wrap());
+}