Revert "Move dart2js from sdk/lib/_internal/compiler to pkg/compiler"

tests/compiler/dart2js/part_of_test.dart

 // Copyright (c) 2013, 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 part_of_test;
 
 import "package:expect/expect.dart";
 import "package:async_helper/async_helper.dart";
 import 'mock_compiler.dart';
-import 'package:compiler/src/dart2jslib.dart'
+import 'package:compiler/implementation/dart2jslib.dart'
     show MessageKind;
 
 final libraryUri = Uri.parse('test:library.dart');
 const String LIBRARY_SOURCE = '''
 library foo;
 part 'part.dart';
 ''';
 
 final partUri = Uri.parse('test:part.dart');
 const String PART_SOURCE = '''
 part of bar;
 ''';
 
 void main() {
   MockCompiler compiler = new MockCompiler.internal();
   compiler.registerSource(libraryUri, LIBRARY_SOURCE);
   compiler.registerSource(partUri, PART_SOURCE);
 
   asyncTest(() => compiler.libraryLoader.loadLibrary(libraryUri).then((_) {
     print('errors: ${compiler.errors}');
     print('warnings: ${compiler.warnings}');
     Expect.isTrue(compiler.errors.isEmpty);
     Expect.equals(1, compiler.warnings.length);
     Expect.equals(MessageKind.LIBRARY_NAME_MISMATCH,
                   compiler.warnings[0].message.kind);
     Expect.equals('foo',
         compiler.warnings[0].message.arguments['libraryName'].toString());
   }));
 }