Pass in `this` as a free variable to the closure class

tests/compiler/dart2js/equivalence/id_equivalence.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:compiler/src/common.dart';
 import 'package:compiler/src/elements/elements.dart';
 import 'package:compiler/src/resolution/access_semantics.dart';
 import 'package:compiler/src/resolution/send_structure.dart';
 import 'package:compiler/src/resolution/tree_elements.dart';
 import 'package:compiler/src/tree/nodes.dart' as ast;
@@ skipping 103 matching lines @@
     String memberName = element.name;
     if (element.isSetter) {
       memberName += '=';
     }
     String className = element.enclosingClass?.name;
     return new ElementId.internal(memberName, className);
   }
 
   NodeId computeAccessId(ast.Send node, AccessSemantics access) {
     switch (access.kind) {
+      case AccessKind.THIS_PROPERTY:
       case AccessKind.DYNAMIC_PROPERTY:
       case AccessKind.LOCAL_VARIABLE:
       case AccessKind.FINAL_LOCAL_VARIABLE:
       case AccessKind.LOCAL_FUNCTION:
       case AccessKind.PARAMETER:
       case AccessKind.FINAL_PARAMETER:
       case AccessKind.EXPRESSION:
         return computeDefaultNodeId(node.selector);
       default:
         return null;
@@ skipping 253 matching lines @@
   visitSwitchCase(ir.SwitchCase node) {
     computeForNode(node, computeSwitchCaseNodeId(node));
     super.visitSwitchCase(node);
   }
 
   visitContinueSwitchStatement(ir.ContinueSwitchStatement node) {
     computeForNode(node, computeGotoNodeId(node));
     super.visitContinueSwitchStatement(node);
   }
 }