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

tests/compiler/dart2js/lookup_member_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 subtype_test;
 
 import 'package:expect/expect.dart';
 import "package:async_helper/async_helper.dart";
 import 'type_test_helper.dart';
-import 'package:compiler/src/dart_types.dart';
-import "package:compiler/src/elements/elements.dart"
+import 'package:compiler/implementation/dart_types.dart';
+import "package:compiler/implementation/elements/elements.dart"
        show Element, ClassElement, MemberSignature, PublicName;
 
 void main() {
   test();
 }
 
 void test() {
   asyncTest(() => TypeEnvironment.create(r"""
       class A<T> {
         T foo;
@@ skipping 48 matching lines @@
     expect(C_U, 'boz', instantiate(B, [U]));
 
     DartType C_int = instantiate(C, [int_]);
     expect(C_int, 'foo', instantiate(A, [String_]));
     expect(C_int, 'bar', String_);
     expect(C_int, 'baz', int_);
     expect(C_int, 'boz', instantiate(B, [int_]));
   }));
 }