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

pkg/compiler/lib/src/scanner/scannerlib.dart

Index: pkg/compiler/lib/src/scanner/scannerlib.dart
diff --git a/pkg/compiler/lib/src/scanner/scannerlib.dart b/pkg/compiler/lib/src/scanner/scannerlib.dart
index b32b5c866e5b8719f1a176d2f646acf5fe6816aa..e4058c8fe4c749e9bb98c6d6aa6e2b97456d8426 100644
--- a/pkg/compiler/lib/src/scanner/scannerlib.dart
+++ b/pkg/compiler/lib/src/scanner/scannerlib.dart
@@ -11,9 +11,10 @@ import '../common/tasks.dart' show
 import '../compiler.dart' show
     Compiler;
 import '../dart_types.dart' show DynamicType;
-import '../diagnostic_listener.dart';
+import '../diagnostics/diagnostic_listener.dart';
 import '../diagnostics/invariant.dart' show
     invariant;
+import '../diagnostics/messages.dart';
 import '../diagnostics/spannable.dart' show
     Spannable,
     SpannableAssertionFailure;
@@ -40,7 +41,6 @@ import '../elements/modelx.dart' show
 
 import '../elements/visitor.dart'
     show ElementVisitor;
-import '../messages.dart';
 import '../native/native.dart' as native;
 import '../string_validator.dart';
 import '../script.dart';