Add boxing for modified variables

pkg/compiler/lib/src/closure.dart

 // Copyright (c) 2012, 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 'common/names.dart' show Identifiers;
 import 'common/resolution.dart' show ParsingContext, Resolution;
 import 'common/tasks.dart' show CompilerTask, Measurer;
 import 'common.dart';
 import 'compiler.dart' show Compiler;
 import 'constants/expressions.dart';
@@ skipping 523 matching lines @@
 
   accept(ElementVisitor visitor, arg) {
     return visitor.visitClosureClassElement(this, arg);
   }
 }
 
 /// A local variable that contains the box object holding the [BoxFieldElement]
 /// fields.
 class BoxLocal extends Local {
   final String name;
-  final Entity executableContext;
   final MemberEntity memberContext;
 
   final int hashCode = _nextHashCode = (_nextHashCode + 10007).toUnsigned(30);
   static int _nextHashCode = 0;
 
-  BoxLocal(this.name, this.executableContext, this.memberContext);
+  BoxLocal(this.name, this.memberContext);
+
+  Entity get executableContext => memberContext;
 
   String toString() => 'BoxLocal($name)';
 }
 
 // TODO(ngeoffray, ahe): These classes continuously cause problems.  We need to
 // find a more general solution.
 class BoxFieldElement extends ElementX
     implements TypedElement, FieldElement, PrivatelyNamedJSEntity {
   final LocalVariableElement variableElement;
   final BoxLocal box;
@@ skipping 692 matching lines @@
   void attachCapturedScopeVariables(Node node) {
     BoxLocal box = null;
     Map<LocalVariableElement, BoxFieldElement> scopeMapping =
         new Map<LocalVariableElement, BoxFieldElement>();
 
     void boxCapturedVariable(LocalVariableElement variable) {
       if (isCapturedVariable(variable)) {
         if (box == null) {
           // TODO(floitsch): construct better box names.
           String boxName = getBoxFieldName(closureFieldCounter++);
-          box = new BoxLocal(
-              boxName, executableContext, executableContext.memberContext);
+          box = new BoxLocal(boxName, executableContext.memberContext);
         }
         String elementName = variable.name;
         String boxedName =
             getClosureVariableName(elementName, boxedFieldCounter++);
         // TODO(kasperl): Should this be a FieldElement instead?
         BoxFieldElement boxed = new BoxFieldElement(boxedName, variable, box);
         scopeMapping[variable] = boxed;
         setCapturedVariableBoxField(variable, boxed);
       }
     }
@@ skipping 277 matching lines @@
 ///
 /// Move the below classes to a JS model eventually.
 ///
 abstract class JSEntity implements MemberEntity {
   Local get declaredEntity;
 }
 
 abstract class PrivatelyNamedJSEntity implements JSEntity {
   Entity get rootOfScope;
 }