Migrate block 163 to Dart 2.0.

tests/language_strong/unary_plus_negative_test.dart

Index: tests/language_strong/unary_plus_negative_test.dart
diff --git a/tests/language_strong/unary_plus_negative_test.dart b/tests/language_strong/unary_plus_negative_test.dart
deleted file mode 100644
index 9f68d8ad7eb089d5a2a39d45f6fefcf5c3f8b156..0000000000000000000000000000000000000000
--- a/tests/language_strong/unary_plus_negative_test.dart
+++ /dev/null
@@ -1,10 +0,0 @@
-// 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.
-
-// There is no unary plus operator in Dart.
-
-main() {
-  var a = 1;
-  var b = +a;
-}