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

pkg/compiler/lib/src/patch_parser.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.
 
 /**
  * This library contains the infrastructure to parse and integrate patch files.
  *
  * Three types of elements can be patched: [LibraryElement], [ClassElement],
  * [FunctionElement]. Patches are introduced in patch libraries which are loaded
  * together with the corresponding origin library. Which libraries that are
@@ skipping 104 matching lines @@
 library patchparser;
 
 import 'dart:async';
 
 import 'constants/values.dart' show
     ConstantValue;
 import 'compiler.dart' show
     Compiler;
 import 'common/tasks.dart' show
     CompilerTask;
-import 'diagnostic_listener.dart';
+import 'diagnostics/diagnostic_listener.dart';
+import 'diagnostics/messages.dart' show
+    MessageKind;
 import 'elements/elements.dart';
 import 'elements/modelx.dart' show
     BaseFunctionElementX,
     ClassElementX,
     GetterElementX,
     LibraryElementX,
     MetadataAnnotationX,
     SetterElementX;
-import 'messages.dart' show
-    MessageKind;
 import 'library_loader.dart' show
     LibraryLoader;
 import 'scanner/scannerlib.dart';  // Scanner, Parsers, Listeners
 import 'script.dart';
 import 'util/util.dart';
 
 class PatchParserTask extends CompilerTask {
   final String name = "Patching Parser";
 
   PatchParserTask(Compiler compiler): super(compiler);
@@ skipping 428 matching lines @@
 
 class PatchVersion {
   final String tag;
 
   const PatchVersion(this.tag);
 
   bool isActive(String patchTag) => tag == null || tag == patchTag;
 
   String toString() => 'PatchVersion($tag)';
 }