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

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 597 matching lines @@
   @override
   bool get hasConstant => false;
 
   @override
   ConstantExpression get constant => null;
 }
 
 /// A local variable used encode the direct (uncaptured) references to [this].
 class ThisLocal extends Local {
   final MemberEntity memberContext;
-  final hashCode = ElementX.newHashCode();
 
   ThisLocal(this.memberContext);
 
   Entity get executableContext => memberContext;
 
   String get name => 'this';
 
   ClassEntity get enclosingClass => memberContext.enclosingClass;
+
+  bool operator ==(other) {
+    return other is ThisLocal &&
+        other.name == name &&
+        other.memberContext == memberContext &&
+        other.enclosingClass == enclosingClass;
+  }
+
+  int get hashCode => memberContext.hashCode + enclosingClass.hashCode;
 }
 
 /// Call method of a closure class.
 // ignore: STRONG_MODE_INVALID_METHOD_OVERRIDE_FROM_BASE
 class SynthesizedCallMethodElementX extends BaseFunctionElementX
     implements MethodElement {
   final LocalFunctionElement expression;
   final FunctionExpression node;
   final TreeElements treeElements;
 
@@ skipping 915 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;
 }