Deprecate the ChainHandler typedef.

lib/src/stack_zone_specification.dart

Index: lib/src/stack_zone_specification.dart
diff --git a/lib/src/stack_zone_specification.dart b/lib/src/stack_zone_specification.dart
index 25d96427110f76a22b134fbaa2634025225434cd..6de43fae8cd8e23a0d6057b824af6084eed32316 100644
--- a/lib/src/stack_zone_specification.dart
+++ b/lib/src/stack_zone_specification.dart
@@ -9,6 +9,9 @@ import 'dart:async';
 import 'trace.dart';
 import 'chain.dart';
 
+/// A function that handles errors in the zone wrapped by [Chain.capture].
+typedef void _ChainHandler(error, Chain chain);
+
 /// A class encapsulating the zone specification for a [Chain.capture] zone.
 ///
 /// Until they're materialized and exposed to the user, stack chains are tracked
@@ -43,7 +46,7 @@ class StackZoneSpecification {
   ///
   /// If this is null, that indicates that any unhandled errors should be passed
   /// to the parent zone.
-  final ChainHandler _onError;
+  final _ChainHandler _onError;
 
   /// The most recent node of the current stack chain.
   _Node _currentNode;