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

tests/compiler/dart2js/reexport_handled_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 reexport_handled_test;
 
 import "package:expect/expect.dart";
 import "package:async_helper/async_helper.dart";
 import 'mock_compiler.dart';
-import 'package:compiler/implementation/elements/elements.dart'
+import 'package:compiler/src/elements/elements.dart'
     show Element,
          LibraryElement;
 
 final exportingLibraryUri = Uri.parse('exporting.dart');
 const String EXPORTING_LIBRARY_SOURCE = '''
 library exporting;
 var foo;
 ''';
 
 final reexportingLibraryUri = Uri.parse('reexporting.dart');
@@ skipping 25 matching lines @@
 }
 
 Element findInExports(LibraryElement library, String name) {
   for (var export in library.exports) {
     if (export.name == name) {
       return export;
     }
   }
   return null;
 }