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

pkg/compiler/lib/src/kernel/element_map_impl.dart

Index: pkg/compiler/lib/src/kernel/element_map_impl.dart
diff --git a/pkg/compiler/lib/src/kernel/element_map_impl.dart b/pkg/compiler/lib/src/kernel/element_map_impl.dart
index 08d470cb96c72dec0178ac673d1d892362287b94..9580ab469dad89c44fa8682fc8a43f54d9f80826 100644
--- a/pkg/compiler/lib/src/kernel/element_map_impl.dart
+++ b/pkg/compiler/lib/src/kernel/element_map_impl.dart
@@ -31,6 +31,7 @@ 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';
@@ -2319,10 +2320,17 @@ class JsKernelToElementMap extends KernelToElementMapBase
       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),
@@ -2333,9 +2341,9 @@ class JsKernelToElementMap extends KernelToElementMapBase
     _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;