Issue 25542. If an element does not have its own documentation, use the documentation from the over…

pkg/analysis_server/test/analysis/notification_overrides_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.
 
 library test.analysis.notification.overrides;
 
 import 'dart:async';
 
 import 'package:analysis_server/plugin/protocol/protocol.dart';
 import 'package:analysis_server/src/constants.dart';
@@ skipping 352 matching lines @@
 }
 class B extends A {
   m() {} // in B
 }
 class C implements B {
   m() {} // in C
 }
 ''');
     await prepareOverrides();
     assertHasOverride('m() {} // in C');
-    expect(override.interfaceMembers, hasLength(1));
+    expect(override.interfaceMembers, hasLength(2));
     assertHasInterfaceMember('m() {} // in B');
   }
 
   test_mix_sameMethod() async {
     addTestFile('''
 class A {
   m() {} // in A
 }
 abstract class B extends A {
 }
@@ skipping 184 matching lines @@
 class B extends A {
   set fff(x) {} // in B
 }
 ''');
     await prepareOverrides();
     assertHasOverride('fff(x) {} // in B');
     assertHasSuperElement('fff(x) {} // in A');
     assertNoInterfaceMembers();
   }
 }