Report when members indirectly inherited through a mixin are not implemented (issue 26411)

tests/language/mixin_of_mixin_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.
 // SharedOptions=--supermixin
 
 // Validate the following text from section 12 ("Mixins") of the spec:
 //
 //     "A mixin application of the form S with M; defines a class C ...
 //     ... C declares the same instance members as M ..."
 //
@@ skipping 16 matching lines @@
 class M2 extends M1 { m2() => null; }
 class M3 extends A with B, C { m3() => null; }
 class T1 = D with M1; // declares c()
 class T2 = D with M2; // declares m2()
 class T3 = D with M3; // declares m3()
 class T4 extends D with M1 {} // extends a class which declares c()
 class T5 extends D with M2 {} // extends a class which declares m2()
 class T6 extends D with M3 {} // extends a class which declares m3()
 
 main() {
+  /// none: static type warning, ok
   new T1().a();  /// 01: static type warning, runtime error
   new T1().b();  /// 02: static type warning, runtime error
-  new T1().c();  /// 03: ok
+  new T1().c();  /// 03: static type warning, ok
   new T2().a();  /// 04: static type warning, runtime error
   new T2().b();  /// 05: static type warning, runtime error
   new T2().c();  /// 06: static type warning, runtime error
-  new T2().m2(); /// 07: ok
+  new T2().m2(); /// 07: static type warning, ok
   new T3().a();  /// 08: static type warning, runtime error
   new T3().b();  /// 09: static type warning, runtime error
   new T3().c();  /// 10: static type warning, runtime error
-  new T3().m3(); /// 11: ok
+  new T3().m3(); /// 11: static type warning, ok
   new T4().a();  /// 12: static type warning, runtime error
   new T4().b();  /// 13: static type warning, runtime error
-  new T4().c();  /// 14: ok
+  new T4().c();  /// 14: static type warning, ok
   new T5().a();  /// 15: static type warning, runtime error
   new T5().b();  /// 16: static type warning, runtime error
   new T5().c();  /// 17: static type warning, runtime error
-  new T5().m2(); /// 18: ok
+  new T5().m2(); /// 18: static type warning, ok
   new T6().a();  /// 19: static type warning, runtime error
   new T6().b();  /// 20: static type warning, runtime error
   new T6().c();  /// 21: static type warning, runtime error
-  new T6().m3(); /// 22: ok
+  new T6().m3(); /// 22: static type warning, ok
 }