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

pkg/compiler/lib/src/compiler.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 dart2js.compiler_base;
 
 import 'dart:async' show
     EventSink,
     Future;
 
@@ skipping 22 matching lines @@
     CoreTypes;
 import 'cps_ir/cps_ir_builder_task.dart' show
     IrBuilderTask;
 import 'dart_backend/dart_backend.dart' as dart_backend;
 import 'dart_types.dart' show
     DartType,
     DynamicType,
     InterfaceType,
     Types;
 import 'deferred_load.dart' show DeferredLoadTask, OutputUnit;
-import 'diagnostic_listener.dart';
 import 'diagnostics/code_location.dart';
+import 'diagnostics/diagnostic_listener.dart';
 import 'diagnostics/invariant.dart' show
     invariant,
     REPORT_EXCESS_RESOLUTION;
+import 'diagnostics/messages.dart' show
+    Message,
+    MessageKind,
+    MessageTemplate;
 import 'diagnostics/source_span.dart' show
     SourceSpan;
 import 'diagnostics/spannable.dart' show
     CURRENT_ELEMENT_SPANNABLE,
     NO_LOCATION_SPANNABLE,
     Spannable,
     SpannableAssertionFailure;
 import 'dump_info.dart' show
     DumpInfoTask;
 import 'elements/elements.dart';
@@ skipping 14 matching lines @@
     QueueFilter,
     WorldImpact;
 import 'io/source_information.dart' show
     SourceInformation;
 import 'js_backend/js_backend.dart' as js_backend show
     JavaScriptBackend;
 import 'library_loader.dart' show
     LibraryLoader,
     LibraryLoaderTask,
     LoadedLibraries;
-import 'messages.dart' show
-    Message,
-    MessageKind,
-    MessageTemplate;
 import 'mirrors_used.dart' show
     MirrorUsageAnalyzerTask;
 import 'null_compiler_output.dart' show
     NullCompilerOutput,
     NullSink;
 import 'patch_parser.dart' show
     PatchParserTask;
 import 'resolution/resolution.dart' show
     ResolutionRegistry,
     ResolverTask,
@@ skipping 1664 matching lines @@
 
   @override
   InterfaceType streamType([DartType elementType]) {
     InterfaceType type = streamClass.computeType(compiler);
     if (elementType == null) {
       return streamClass.rawType;
     }
     return type.createInstantiation([elementType]);
   }
 }