Fix the locals lookup of variables and partial implementation of boxing of variables.

pkg/compiler/lib/src/js_model/elements.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.js_model.elements;
 
 import '../common/names.dart' show Names;
 import '../elements/entities.dart';
 import '../elements/names.dart';
 import '../elements/types.dart';
@@ skipping 301 matching lines @@
   final JLibrary library;
 
   /// Class index used for fast lookup in [JsToFrontendMapImpl].
   final int classIndex;
 
   final String name;
   final bool isAbstract;
 
   JClass(this.library, this.classIndex, this.name, {this.isAbstract});
 
-  @override
+  /// True if this class is a class created to represent the semantics of a Dart
+  /// closure.
   bool get isClosure => false;
 
   String toString() => '${jsElementPrefix}class($name)';
 }
 
 class JTypedef implements TypedefEntity, IndexedTypedef {
   final JLibrary library;
 
   /// Typedef index used for fast lookup in [JsToFrontendMapImpl].
   final int typedefIndex;
@@ skipping 207 matching lines @@
 
   @override
   bool get isField => true;
 
   String get _kind => 'field';
 }
 
 class JClosureCallMethod extends JMethod {
   JClosureCallMethod(int memberIndex, KernelClosureClass containingClass,
       ParameterStructure parameterStructure, AsyncMarker asyncMarker)
-      : super(memberIndex, containingClass.library, containingClass, Names.call,
-            parameterStructure, asyncMarker,
-            isStatic: false, isExternal: false, isAbstract: false);
+      : super(
+            memberIndex,
+            containingClass.closureClassEntity.library,
+            containingClass.closureClassEntity,
+            Names.call,
+            parameterStructure,
+            asyncMarker,
+            isStatic: false,
+            isExternal: false,
+            isAbstract: false);
 
   String get _kind => 'closure_call';
 }
 
 class JTypeVariable implements TypeVariableEntity, IndexedTypeVariable {
   final int typeVariableIndex;
   final Entity typeDeclaration;
   final String name;
   final int index;
 
   JTypeVariable(
       this.typeVariableIndex, this.typeDeclaration, this.name, this.index);
 
   String toString() =>
       '${jsElementPrefix}type_variable(${typeDeclaration.name}.$name)';
 }