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

pkg/compiler/lib/src/kernel/element_map_impl.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.kernel.element_map;
 
 import 'package:kernel/ast.dart' as ir;
 
 import '../closure.dart' show BoxLocal, ThisLocal;
 import '../common.dart';
@@ skipping 13 matching lines @@
 import '../elements/types.dart';
 import '../environment.dart';
 import '../frontend_strategy.dart';
 import '../js_backend/backend_usage.dart';
 import '../js_backend/constant_system_javascript.dart';
 import '../js_backend/interceptor_data.dart';
 import '../js_backend/native_data.dart';
 import '../js_backend/no_such_method_registry.dart';
 import '../js_backend/runtime_types.dart';
 import '../js_model/closure.dart';
+import '../js_model/closure_visitors.dart' show ThisVariable;
 import '../js_model/elements.dart';
 import '../js_model/locals.dart';
 import '../native/enqueue.dart';
 import '../native/native.dart' as native;
 import '../native/resolver.dart';
 import '../ordered_typeset.dart';
 import '../options.dart';
 import '../ssa/kernel_impact.dart';
 import '../universe/class_set.dart';
 import '../universe/selector.dart';
@@ skipping 2268 matching lines @@
 
   _constructClosureField(
       MemberEntity member,
       KernelClosureClass cls,
       Map<String, MemberEntity> memberMap,
       ir.VariableDeclaration variable,
       Map<Local, JRecordField> boxedCapturedVariables,
       int fieldNumber,
       NodeBox box,
       KernelToLocalsMap localsMap) {
-    // NOTE: This construction order may be slightly different than the
+    // NOTE: This construction *order* may be slightly different than the
     // old Element version. The old version did all the boxed items and then
     // all the others.
-    Local capturedLocal = localsMap.getLocalVariable(variable);
+    ir.Node sourceNode = variable;
+    Local capturedLocal;
+    if (variable is ThisVariable) {
+      capturedLocal = cls.thisLocal;
+      sourceNode = getMemberDefinition(member).node;
+    } else {
+      capturedLocal = localsMap.getLocalVariable(variable);
+    }
     JRecordField field = boxedCapturedVariables[capturedLocal];
     FieldEntity closureField = new JClosureField(
         _getClosureVariableName(capturedLocal.name, fieldNumber),
         _memberData.length,
         cls,
         variable.isConst,
         variable.isFinal || variable.isConst);
     _memberList.add(closureField);
     _memberData.add(new ClosureFieldData(new ClosureMemberDefinition(
         cls.localToFieldMap[capturedLocal],
-        computeSourceSpanFromTreeNode(variable),
+        computeSourceSpanFromTreeNode(sourceNode),
         MemberKind.closureField,
-        variable)));
+        sourceNode)));
     memberMap[closureField.name] = closureField;
     if (boxedCapturedVariables.containsKey(capturedLocal)) {
       cls.localToFieldMap[field.box] = closureField;
       cls.boxedVariables[capturedLocal] = field;
     } else {
       cls.localToFieldMap[capturedLocal] = closureField;
     }
   }
 
   // Returns a non-unique name for the given closure element.
@@ skipping 44 matching lines @@
   ///
   /// These names are not used in generated code, just as element name.
   String _getClosureVariableName(String name, int id) {
     return "_captured_${name}_$id";
   }
 
   String getDeferredUri(ir.LibraryDependency node) {
     throw new UnimplementedError('JsKernelToElementMap.getDeferredUri');
   }
 }