Remove warning for inherited noSuchMethod.

tests/language/proxy4_test.dart

+// Copyright (c) 2016, 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.
+
+// Test for static warnings for member access on classes that inherit a
+// user defined noSuchMethod.
+
+class Mock {
+  noSuchMethod(i) => 42;
+}
+
+abstract class Foo { int foo(); }
+
+class DontWarnMe extends Mock implements Foo {}
+
+main() {
+  print(new DontWarnMe().foo());
+}