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

pkg/compiler/lib/src/deferred_load.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 deferred_load;
 
 import 'common/backend_api.dart' show
     Backend;
 import 'common/tasks.dart' show
     CompilerTask;
 import 'compiler.dart' show
     Compiler;
 import 'constants/values.dart' show
     ConstantValue,
     ConstructedConstantValue,
     DeferredConstantValue,
     StringConstantValue;
 import 'dart_types.dart';
+import 'diagnostics/messages.dart' show
+    MessageKind;
 import 'elements/elements.dart' show
     AccessorElement,
     AstElement,
     ClassElement,
     Element,
     ElementKind,
     Elements,
     FunctionElement,
     LibraryElement,
     MetadataAnnotation,
     PrefixElement,
     ScopeContainerElement,
     TypedefElement,
     VoidElement;
 import 'js_backend/js_backend.dart' show
     JavaScriptBackend;
-import 'messages.dart' show
-    MessageKind;
 import 'resolution/resolution.dart' show
     AnalyzableElementX,
     TreeElements;
 import 'tree/tree.dart' as ast;
 import 'tree/tree.dart' show
     Import,
     LibraryTag,
     LibraryDependency,
     LiteralDartString,
     LiteralString,
@@ skipping 836 matching lines @@
         _importingLibrary = importingLibrary;
 
   String get importingLibraryName {
     String libraryName = _importingLibrary.getLibraryName();
     return libraryName == ""
       ? "<unnamed>"
       : libraryName;
   }
 
 }