Add boxing for modified variables

pkg/compiler/lib/src/kernel/element_map.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.
 
 import 'package:kernel/ast.dart' as ir;
 
 import '../closure.dart';
 import '../common.dart';
 import '../constants/values.dart';
 import '../common_elements.dart';
 import '../elements/entities.dart';
 import '../elements/jumps.dart';
 import '../elements/names.dart';
 import '../elements/types.dart';
 import '../js/js.dart' as js;
 import '../js_backend/namer.dart';
 import '../js_backend/native_data.dart';
 import '../js_emitter/code_emitter_task.dart';
+import '../js_model/closure.dart' show JRecordField, KernelScopeInfo;
 import '../native/native.dart' as native;
 import '../types/types.dart';
 import '../universe/call_structure.dart';
 import '../universe/selector.dart';
 import '../world.dart';
 
 /// Interface that translates between Kernel IR nodes and entities.
 abstract class KernelToElementMap {
   /// Access to the commonly used elements and types.
   CommonElements get commonElements;
@@ skipping 167 matching lines @@
   /// context of [member].
   Spannable getSpannable(MemberEntity member, ir.Node node);
 
   /// Returns the constructor body entity corresponding to [constructor].
   FunctionEntity getConstructorBody(ir.Constructor node);
 
   /// Returns the uri for the deferred import [node].
   // TODO(johnniwinther): Avoid this method by deriving the uri directly from
   // the node.
   String getDeferredUri(ir.LibraryDependency node);
+
+  /// Make a record to ensure variables that are are declared in one scope and
+  /// modified in another get their values updated correctly.
+  Map<Local, JRecordField> makeRecordContainer(
+      KernelScopeInfo info, MemberEntity member, KernelToLocalsMap localsMap);
 }
 
 // TODO(johnniwinther,efortuna): Add more when needed.
 // TODO(johnniwinther): Should we split regular into method, field, etc.?
 enum MemberKind {
   // A regular member defined by an [ir.Node].
   regular,
   // A constructor whose initializer is defined by an [ir.Constructor] node.
   constructor,
   // A constructor whose body is defined by an [ir.Constructor] node.
@@ skipping 250 matching lines @@
       uri = Uri.parse(node.location.file);
       break;
     }
     node = node.parent;
   }
   if (uri != null) {
     return new SourceSpan(uri, offset, offset + 1);
   }
   return null;
 }