Move diagnostic_listener.dart and messages.dart to the diagnostics folder

pkg/compiler/lib/src/resolution/class_members.dart

 // Copyright (c) 2012, 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 resolution.compute_members;
 
 import '../compiler.dart' show
     Compiler,
     isPrivateName;
 import '../dart_types.dart';
 import '../diagnostics/invariant.dart' show
     invariant;
+import '../diagnostics/messages.dart' show
+    MessageKind;
 import '../elements/elements.dart' show
     ClassElement,
     Element,
     LibraryElement,
     Member,
     MemberElement,
     MemberSignature,
     MixinApplicationElement,
     Name,
     PublicName;
-import '../messages.dart' show
-    MessageKind;
 import '../util/util.dart';
 
 part 'member_impl.dart';
 
 abstract class MembersCreator {
   final ClassElement cls;
   final Compiler compiler;
 
   final Iterable<String> computedMemberNames;
   final Map<Name, Member> classMembers;
@@ skipping 871 matching lines @@
         message: "Members have not been fully computed for $this."));
     if (interfaceMembersAreClassMembers) {
       classMembers.forEach((_, member) {
         if (!member.isStatic) f(member);
       });
     } else {
       interfaceMembers.forEach((_, member) => f(member));
     }
   }
 }