Fix an off by one AST node error, when fetching the type of a new List constructor.

tests/compiler/dart2js/list_tracer_node_type_test.dart

Index: tests/compiler/dart2js/list_tracer_node_type_test.dart
===================================================================
--- tests/compiler/dart2js/list_tracer_node_type_test.dart	(revision 0)
+++ tests/compiler/dart2js/list_tracer_node_type_test.dart	(revision 0)
@@ -0,0 +1,48 @@
+// 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.
+
+import "package:expect/expect.dart";
+import 'compiler_helper.dart';
+
+const String TEST1 = r"""
+main() {
+  var a = [42, null];
+  return a[0] + 42;
+}
+""";
+
+const String TEST2 = r"""
+main() {
+  var a = new List();
+  a.add(42);
+  a.add(null);
+  return a[0] + 42;
+}
+""";
+
+const String TEST3 = r"""
+main() {
+  var a = new List(42);
+  a[0] = 42;
+  return a[0] + 42;
+}
+""";
+
+
+main() {
+  String generated = compileAll(TEST1);
+  // Check that we only do a null check on the receiver for
+  // [: a[0] + 42 :]. We can do a null check because we inferred that
+  // the list is of type int or null.
+  Expect.isFalse(generated.contains('if (typeof t1'));
+  Expect.isTrue(generated.contains('if (t1 == null)'));
+
+  generated = compileAll(TEST2);
+  Expect.isFalse(generated.contains('if (typeof t1'));
+  Expect.isTrue(generated.contains('if (t1 == null)'));
+
+  generated = compileAll(TEST3);
+  Expect.isFalse(generated.contains('if (typeof t1'));
+  Expect.isTrue(generated.contains('if (t1 == null)'));
+}