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

pkg/compiler/lib/src/js_model/closure.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 '../common/tasks.dart';
 import '../constants/expressions.dart';
@@ skipping 235 matching lines @@
   final bool hasThisLocal;
   final Set<ir.VariableDeclaration> boxedVariables;
   // If boxedVariables is empty, this will be null, because no variables will
   // need to be boxed.
   final NodeBox capturedVariablesAccessor;
 
   /// The set of variables that were defined in another scope, but are used in
   /// this scope.
   Set<ir.VariableDeclaration> freeVariables = new Set<ir.VariableDeclaration>();
 
+  /// If true, `this` is used as a free variable, in this scope. It is stored
+  /// separately from [freeVariables] because there is no single
+  /// `VariableDeclaration` node that represents `this`.
+  bool thisUsedAsFreeVariable = false;
+
   KernelScopeInfo(this.hasThisLocal)
       : localsUsedInTryOrSync = new Set<ir.VariableDeclaration>(),
         boxedVariables = new Set<ir.VariableDeclaration>(),
         capturedVariablesAccessor = null;
 
   KernelScopeInfo.from(this.hasThisLocal, KernelScopeInfo info)
       : localsUsedInTryOrSync = info.localsUsedInTryOrSync,
         boxedVariables = info.boxedVariables,
         capturedVariablesAccessor = null;
 
@@ skipping 21 matching lines @@
   /// this scope.
   final Set<Local> freeVariables;
 
   JsScopeInfo.from(
       this.boxedVariables, KernelScopeInfo info, KernelToLocalsMap localsMap)
       : this.thisLocal =
             info.hasThisLocal ? new ThisLocal(localsMap.currentMember) : null,
         this.localsUsedInTryOrSync =
             info.localsUsedInTryOrSync.map(localsMap.getLocalVariable).toSet(),
         this.freeVariables =
-            info.freeVariables.map(localsMap.getLocalVariable).toSet();
+            info.freeVariables.map(localsMap.getLocalVariable).toSet() {
+    if (info.thisUsedAsFreeVariable) {
+      this.freeVariables.add(this.thisLocal);
+    }
+  }
 
   void forEachBoxedVariable(f(Local local, FieldEntity field)) {
     boxedVariables.forEach((Local l, JRecordField box) {
       f(l, box);
     });
   }
 
   bool localIsUsedInTryOrSync(Local variable) =>
       localsUsedInTryOrSync.contains(variable);
 
@@ skipping 311 matching lines @@
   KernelScopeInfo scopeInfo;
 
   /// Collected [CapturedScope] data for nodes.
   Map<ir.Node, KernelCapturedScope> capturedScopesMap =
       <ir.Node, KernelCapturedScope>{};
 
   /// Collected [ScopeInfo] data for nodes.
   Map<ir.TreeNode, KernelScopeInfo> closuresToGenerate =
       <ir.TreeNode, KernelScopeInfo>{};
 }