Parameterize and move JumpTarget/LabelDefition to elements/jumps.dart

pkg/compiler/lib/src/kernel/kernel_backend_strategy.dart

 // Copyright (c) 2017, 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 dart2js.kernel.backend_strategy;
 
 import 'package:kernel/ast.dart' as ir;
 
 import '../backend_strategy.dart';
 import '../closure.dart';
 import '../common/codegen.dart' show CodegenRegistry, CodegenWorkItem;
 import '../common/tasks.dart';
 import '../compiler.dart';
-import '../elements/elements.dart' show JumpTarget;
 import '../elements/entities.dart';
 import '../elements/entity_utils.dart' as utils;
+import '../elements/jumps.dart';
 import '../enqueue.dart';
 import '../io/source_information.dart';
 import '../js/js_source_mapping.dart';
 import '../js_backend/backend.dart';
 import '../js_backend/native_data.dart';
 import '../js_emitter/sorter.dart';
 import '../kernel/element_map.dart';
 import '../kernel/element_map_impl.dart';
 import '../native/behavior.dart';
 import '../options.dart';
@@ skipping 347 matching lines @@
   Iterable<ClassEntity> sortClasses(Iterable<ClassEntity> classes) {
     return classes.toList()
       ..sort((ClassEntity a, ClassEntity b) {
         int r = _compareLibraries(a.library, b.library);
         if (r != 0) return r;
         return _compareNodes(
             a, elementMap.getClassNode(a), b, elementMap.getClassNode(b));
       });
   }
 }