Move dart2jslib parts into separate libraries.

tests/compiler/dart2js/backend_dart/dart_printer_test.dart

Index: tests/compiler/dart2js/backend_dart/dart_printer_test.dart
diff --git a/tests/compiler/dart2js/backend_dart/dart_printer_test.dart b/tests/compiler/dart2js/backend_dart/dart_printer_test.dart
index 407b149e2588ebd4a5e5b2cef784060423a47c6e..e7f16a46d7e994ab060172ab077c11fae6cef878 100644
--- a/tests/compiler/dart2js/backend_dart/dart_printer_test.dart
+++ b/tests/compiler/dart2js/backend_dart/dart_printer_test.dart
@@ -10,12 +10,15 @@ import 'package:compiler/src/dart_backend/backend_ast_nodes.dart';
 import 'package:compiler/src/scanner/scannerlib.dart';
 import 'package:compiler/src/io/source_file.dart';
 import 'package:compiler/src/dart2jslib.dart';
+import 'package:compiler/src/diagnostic_listener.dart';
+import "package:compiler/src/messages.dart";
 import 'package:compiler/src/tree/tree.dart' show DartString;
 import 'dart:mirrors';
 import 'package:compiler/src/tree/tree.dart' as tree;
 import 'package:compiler/src/string_validator.dart';
 import 'package:compiler/src/dart_backend/backend_ast_to_frontend_ast.dart'
     show TreePrinter;
+import 'package:compiler/src/util/util.dart' show Spannable;
 
 /// For debugging the [AstBuilder] stack. Prints information about [x].
 void show(x) {