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

tests/compiler/dart2js/mirrors_used_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.
 
 /// Test that the @MirrorsUsed annotation suppress hints and that only
 /// requested elements are retained for reflection.
 library dart2js.test.mirrors_used_test;
 
 import 'package:expect/expect.dart';
 import "package:async_helper/async_helper.dart";
 
 import 'memory_compiler.dart' show
     compilerFor;
 
-import 'package:compiler/src/apiimpl.dart' show
+import 'package:compiler/implementation/apiimpl.dart' show
     Compiler;
 
-import 'package:compiler/src/constants/values.dart' show
+import 'package:compiler/implementation/constants/values.dart' show
     ConstantValue,
     TypeConstantValue;
 
-import 'package:compiler/src/elements/elements.dart' show
+import 'package:compiler/implementation/elements/elements.dart' show
     Element,
     Elements;
 
-import 'package:compiler/src/js_backend/js_backend.dart' show
+import 'package:compiler/implementation/js_backend/js_backend.dart' show
     JavaScriptBackend;
 
 void expectOnlyVerboseInfo(Uri uri, int begin, int end, String message, kind) {
   if (kind.name == 'verbose info') {
     print(message);
     return;
   }
   if (message.contains('methods retained for use by dart:mirrors out of')) {
     print(message);
     return;
@@ skipping 128 matching lines @@
 library lib;
 
 import 'dart:mirrors';
 
 useReflect(type) {
   print(new Symbol('Foo'));
   print(MirrorSystem.getName(reflectClass(type).owner.qualifiedName));
 }
 """,
 };