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

tests/compiler/dart2js/parser_helper.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 parser_helper;
 
 import "package:expect/expect.dart";
 
 import "package:compiler/src/elements/elements.dart";
 import "package:compiler/src/tree/tree.dart";
 import "package:compiler/src/scanner/scannerlib.dart";
 import "package:compiler/src/io/source_file.dart";
 import "package:compiler/src/util/util.dart";
 
 import "package:compiler/src/elements/modelx.dart"
     show CompilationUnitElementX, ElementX, LibraryElementX;
 
 import "package:compiler/src/compiler.dart";
 import "package:compiler/src/diagnostics/source_span.dart";
 import "package:compiler/src/diagnostics/spannable.dart";
-import "package:compiler/src/diagnostic_listener.dart";
-import "package:compiler/src/messages.dart";
+import "package:compiler/src/diagnostics/diagnostic_listener.dart";
+import "package:compiler/src/diagnostics/messages.dart";
 import "package:compiler/src/script.dart";
 
-export "package:compiler/src/diagnostic_listener.dart";
+export "package:compiler/src/diagnostics/diagnostic_listener.dart";
 // TODO(ahe): We should have token library to export instead.
 export "package:compiler/src/scanner/scannerlib.dart";
 
 class LoggerCanceler implements DiagnosticListener {
   void log(message) {
     print(message);
   }
 
   void internalError(node, String message) {
     log(message);
@@ skipping 91 matching lines @@
   ElementListener listener = new ElementListener(compiler, unit, () => id++);
   PartialParser parser = new PartialParser(listener);
   compiler.withCurrentElement(unit, () => parser.parseUnit(tokens));
   return unit.localMembers;
 }
 
 NodeList fullParseUnit(String source, {DiagnosticListener diagnosticHandler}) {
   return parseBodyCode(source, (parser, tokens) => parser.parseUnit(tokens),
                        diagnosticHandler: diagnosticHandler);
 }