Add missing copyright on test cases.

pkg/front_end/testcases/void_methods.dart

Index: pkg/front_end/testcases/void_methods.dart
diff --git a/pkg/front_end/testcases/void_methods.dart b/pkg/front_end/testcases/void_methods.dart
new file mode 100644
index 0000000000000000000000000000000000000000..5e8d6f788525dab17136ade6ca715964aa4eef04
--- /dev/null
+++ b/pkg/front_end/testcases/void_methods.dart
@@ -0,0 +1,16 @@
+// Copyright (c) 2017, 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 Foo {
+  List list = [1, 2, 3];
+  set first(x) => list[0] = x;
+  operator []=(x, y) => list[x] = y;
+  void clear() => list.clear();
+}
+
+main() {
+  new Foo().first = 4;
+  new Foo()[3] = 4;
+  new Foo().clear();
+}