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

tests/compiler/dart2js/least_upper_bound_test.dart

Index: tests/compiler/dart2js/least_upper_bound_test.dart
diff --git a/tests/compiler/dart2js/least_upper_bound_test.dart b/tests/compiler/dart2js/least_upper_bound_test.dart
index 804b8036d64bbd51aa708a33bc683f1fa07625f3..a59a36c6234949a2426f96a618bc05bbd9d466fc 100644
--- a/tests/compiler/dart2js/least_upper_bound_test.dart
+++ b/tests/compiler/dart2js/least_upper_bound_test.dart
@@ -7,10 +7,10 @@ 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;
-import 'package:compiler/src/util/util.dart';
+import 'package:compiler/implementation/util/util.dart';
 
 void main() {
   testInterface1();