Reapply "Add nonboxed closure class fields."

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 2bac7edb2bd15a8818bf81d9a4dbc8eac0f7dbca..82dd2d4d9ec5e521c2c5b59270bc1c204ecabdc5 100644
--- a/pkg/compiler/lib/src/kernel/element_map_impl.dart
+++ b/pkg/compiler/lib/src/kernel/element_map_impl.dart
@@ -687,6 +687,13 @@ abstract class ElementCreatorMixin {
     _classData.add(closureData);
     closureData.orderedTypeSet = setBuilder.createOrderedTypeSet(
         closureData.supertype, const Link<InterfaceType>());
+
+    cls.forEachCapturedVariable((Local local, JField field) {
+      field.setClosureMemberIndex = _memberData.length;
+      // TODO(efortuna): Uncomment this line after Johnni's added in his CL
+      // about Class/MemberDefinition.
+      //_memberData.add(field);
+    });
     // TODO(efortuna): Does getMetadata get called in ClassData for this object?
   }