Move dart2jslib parts into separate libraries.

tests/compiler/dart2js/backend_dart/dart_printer_test.dart

 // Copyright (c) 2014, 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 dart_printer_test;
 
 import "package:expect/expect.dart";
 import 'package:compiler/src/constants/values.dart';
 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) {
   StringBuffer buf = new StringBuffer();
   Unparser unparser = new Unparser(buf);
   void unparse(x) {
     if (x is Expression)
       unparser.writeExpression(x);
     else if (x is TypeAnnotation)
       unparser.writeType(x);
@@ skipping 939 matching lines @@
   checkStatement("do while(x); while (y);");
   checkStatement("{do; while(x); while (y);}");
 
   checkStatement('switch(x) { case 1: case 2: return y; }');
   checkStatement('switch(x) { default: return y; }');
   checkStatement('switch(x) { case 1: x=y; default: return y; }');
   checkStatement('switch(x) { case 1: x=y; y=z; break; default: return y; }');
 
 }