Make closures in constructor initializers read type variables directly.

tests/language/closures_initializer_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.
+
+class A<T> {
+  var t;
+  A() : t = (() => new List<T>());
+}
+
+class B<T> {
+  var t;
+  B() : t = (() => T);
+}
+
+expect(result, expected) {
+  if (result != expected) {
+    throw 'Expected $expected, got $result';
+  }
+}
+
+main() {
+  expect(new A<int>().t() is List<int>, true);
+  expect(new A<String>().t() is List<int>, false);
+  expect(new B<int>().t() is Type, true);
+  expect(new B<int>().t(), int);
+}