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

tests/compiler/dart2js/private_test.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.
 
 import "package:expect/expect.dart";
 import "package:async_helper/async_helper.dart";
 import 'mock_compiler.dart';
 
-import 'package:compiler/src/source_file.dart';
-import 'package:compiler/src/dart2jslib.dart';
+import 'package:compiler/implementation/source_file.dart';
+import 'package:compiler/implementation/dart2jslib.dart';
 
 const String PRIVATE_SOURCE_URI = 'src:private';
 const String PRIVATE_SOURCE = '''
 
 var _privateVariable;
 void _privateFunction() {}
 
 class _PrivateClass {
   _PrivateClass();
   _PrivateClass.publicConstructor();
@@ skipping 137 matching lines @@
   // Call public getter on public class.
   analyze('var value = publicClass.publicGetter;');
   // Call public setter on public class.
   analyze('publicClass.publicSetter = 0;');
   // Access public method on public class.
   analyze('var value = publicClass.publicMethod;');
   // Call public method on public class.
   analyze('publicClass.publicMethod();');
 }