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

tests/compiler/dart2js/map_tracer_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.
 
 import 'package:expect/expect.dart';
 import "package:async_helper/async_helper.dart";
-import 'package:compiler/src/types/types.dart'
+import 'package:compiler/implementation/types/types.dart'
     show MapTypeMask, TypeMask;
 
 import 'compiler_helper.dart';
 import 'parser_helper.dart';
 import 'type_mask_test_helper.dart';
 
 
 String generateTest(String mapAllocation) {
   return """
 int anInt = 42;
@@ skipping 258 matching lines @@
     checkType('mapStoredInListButEscapes', K(typesTask.dynamicType),
                                            V(typesTask.dynamicType));
     checkType('mapStoredInMap', K(aKeyType), V(typesTask.uint31Type));
     checkType('mapStoredInMapButEscapes', K(typesTask.dynamicType),
                                           V(typesTask.dynamicType));
 
     checkType('mapUnset', K(emptyType), V(emptyType));
     checkType('mapOnlySetWithConstraint', K(aKeyType), V(emptyType));
   }));
 }