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

pkg/compiler/lib/src/resolution/resolution.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;
 
 import 'dart:collection' show Queue;
 
 import '../common/backend_api.dart' show
     Backend;
 import '../common/registry.dart' show
     Registry;
 import '../common/tasks.dart' show
     CompilerTask,
     DeferredAction;
 import '../compiler.dart' show
     Compiler,
     isPrivateName;
 import '../compile_time_constants.dart';
 import '../constants/constructors.dart';
 import '../constants/expressions.dart';
 import '../constants/values.dart';
 import '../core_types.dart';
 import '../dart_backend/dart_backend.dart' show DartBackend;
 import '../dart_types.dart';
 import '../diagnostics/invariant.dart' show
     invariant;
+import '../diagnostics/messages.dart' show MessageKind;
 import '../diagnostics/spannable.dart' show
     Spannable;
 import '../enqueue.dart' show
     ResolutionEnqueuer,
     WorldImpact;
 import '../tree/tree.dart';
 import '../scanner/scannerlib.dart';
 import '../elements/elements.dart';
 import '../elements/modelx.dart' show
     BaseClassElementX,
@@ skipping 18 matching lines @@
     MethodElementX,
     MixinApplicationElementX,
     ParameterElementX,
     ParameterMetadataAnnotation,
     SetterElementX,
     SynthesizedConstructorElementX,
     TypeVariableElementX,
     TypedefElementX,
     VariableElementX,
     VariableList;
-import '../messages.dart' show MessageKind;
 import '../ordered_typeset.dart' show OrderedTypeSet, OrderedTypeSetBuilder;
 import '../types/types.dart' show TypeMask;
 import '../util/util.dart';
 import '../universe/universe.dart' show
     CallStructure,
     Selector,
     SelectorKind,
     UniverseSelector;
 import '../world.dart' show World;
 
@@ skipping 10 matching lines @@
 part 'members.dart';
 part 'registry.dart';
 part 'resolution_common.dart';
 part 'resolution_result.dart';
 part 'scope.dart';
 part 'signatures.dart';
 part 'tree_elements.dart';
 part 'typedefs.dart';
 part 'type_resolver.dart';
 part 'variables.dart';