Add missing copyright on test cases.

pkg/front_end/testcases/call.dart

+// 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 Callable {
   call(x) {
     return "string";
   }
 }
 
 class CallableGetter {
   get call => new Callable();
 }
 
@@ skipping 24 matching lines @@
   var nothing5 = callable();
   var nothing6 = callable.call();
   var nothing7 = callable.call.call();
   var nothing8 = callable.call.call.call();
 
   var nothing9 = callableGetter();
   var nothing10 = callableGetter.call();
   var nothing11 = callableGetter.call.call();
   var nothing12 = callableGetter.call.call.call();
 }