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

pkg/compiler/lib/src/dump_info.dart

 // Copyright (c) 2013, 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 dump_info;
 
 import 'dart:convert'
     show HtmlEscape, JsonEncoder, StringConversionSink, ChunkedConversionSink;
 
 import 'common/tasks.dart' show
     CompilerTask;
 import 'compiler.dart' show
     Compiler;
+import 'diagnostics/messages.dart' show
+    MessageKind;
 import 'diagnostics/spannable.dart' show
     NO_LOCATION_SPANNABLE;
 import 'elements/elements.dart';
 import 'elements/visitor.dart';
 import 'types/types.dart' show
     TypeMask;
 import 'deferred_load.dart' show
     OutputUnit;
 import 'info/info.dart';
 import 'js_backend/js_backend.dart' show
     JavaScriptBackend;
 import 'js_emitter/full_emitter/emitter.dart' as full show
     Emitter;
 import 'js/js.dart' as jsAst;
-import 'messages.dart' show
-    MessageKind;
 import 'universe/universe.dart' show
     Selector,
     UniverseSelector;
 
 class ElementInfoCollector extends BaseElementVisitor<Info, dynamic> {
   final Compiler compiler;
 
   final AllInfo result = new AllInfo();
   final Map<Element, Info> _elementToInfo = <Element, Info>{};
   final Map<OutputUnit, OutputUnitInfo> _outputToInfo = {};
@@ skipping 492 matching lines @@
 
     ChunkedConversionSink<Object> sink = encoder.startChunkedConversion(
         new StringConversionSink.fromStringSink(buffer));
     sink.add(result.toJson());
     compiler.reportInfo(NO_LOCATION_SPANNABLE, MessageKind.GENERIC, {
       'text': "View the dumped .info.json file at "
           "https://dart-lang.github.io/dump-info-visualizer"
     });
   }
 }