BREAKING CHANGE: enforce part of directive

tests/language/overridden_no_such_method.dart

 // Copyright (c) 2011, 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.
 // Dart test program testing overridden messageNotUnderstood.
 
+part of ManyOverriddenNoSuchMethodTest.dart;
+
 class GetName {
   foo(a, b) => "foo";
 }
 
 String getName(im) => reflect(new GetName()).delegate(im);
 
 class OverriddenNoSuchMethod {
 
   OverriddenNoSuchMethod() {}
 
   noSuchMethod(Invocation mirror) {
     Expect.equals("foo", getName(mirror));
     // 'foo' was called with two parameters (not counting receiver).
     List args = mirror.positionalArguments;
     Expect.equals(2, args.length);
     Expect.equals(101, args[0]);
     Expect.equals(202, args[1]);
     return 5;
   }
 
   static testMain() {
     var obj = new OverriddenNoSuchMethod();
     Expect.equals(5, obj.foo(101, 202));
   }
 }