Use entities in various ssa helpers.

pkg/compiler/lib/src/ssa/loop_handler.dart

 // Copyright (c) 2016, 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:kernel/ast.dart' as ir;
 
-import '../elements/elements.dart';
+import '../elements/elements.dart' show JumpTarget, LabelDefinition;
 import '../io/source_information.dart';
 import '../tree/tree.dart' as ast;
 
 import 'builder.dart';
 import 'builder_kernel.dart';
 import 'graph_builder.dart';
 import 'jump_handler.dart';
 import 'kernel_ast_adapter.dart';
 import 'locals_handler.dart';
 import 'nodes.dart';
@@ skipping 389 matching lines @@
       HLoopBlockInformation.DO_WHILE_LOOP;
 
   @override
   int visitForInStatement(ir.ForInStatement node) =>
       HLoopBlockInformation.FOR_IN_LOOP;
 
   @override
   int visitSwitchStatement(ir.SwitchStatement node) =>
       HLoopBlockInformation.SWITCH_CONTINUE_LOOP;
 }