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

tests/compiler/dart2js/deferred_follow_constant_dependencies_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.
 
 // Test that constants depended on by other constants are correctly deferred.
 
 import 'dart:async';
 import 'package:async_helper/async_helper.dart';
-import 'package:compiler/src/constants/values.dart';
+import 'package:compiler/implementation/constants/values.dart';
 import 'package:expect/expect.dart';
 import 'memory_source_file_helper.dart';
 
 
 class FakeOutputStream<T> extends EventSink<T> {
   void add(T event) {}
   void addError(T event, [StackTrace stackTrace]) {}
   void close() {}
 }
 
@@ skipping 55 matching lines @@
   print(lib.L);
 }
 """, "lib.dart": """
 class C {
   final a;
   const C(this.a);
 }
 
 const L = const {"cA": const C(const {"cB": "cC"})};
 """,};