Conflicting inheritance from superinterface is not a compile time error

tests/language/override_inheritance_mixed_test.dart

 // Copyright (c) 2014, 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 A {
   var member1; /// 01: compile-time error
   member2() {} /// 02: compile-time error
   get member3 => null; /// 03: compile-time error
   member4() {} /// 04: compile-time error
 }
 
 abstract class I {
   var member5; /// 05: ok
   var member6; /// 06: static type warning
   get member7; /// 07: static type warning
-  get member8; /// 08: compile-time error
-  get member9; /// 09: compile-time error
+  get member8; /// 08: static type warning
+  get member9; /// 09: static type warning
 }
 
 abstract class J {
   get member5; /// 05: continued
   member6() {} /// 06: continued
   member7() {} /// 07: continued
   member8() {} /// 08: continued
   member9() {} /// 09: continued
 }
 
 abstract class B extends A implements I, J {
 }
 
 class Class extends B {
   member1() {} /// 01: continued
   var member2; /// 02: continued
   member3() {} /// 03: continued
   get member4 => null; /// 04: continued
   var member5; /// 05: continued
   member8() {} /// 08: continued
   get member9 => null; /// 09: continued
 }
 
 main() {
   new Class();
 }