Deprecate the ChainHandler typedef.

lib/src/chain.dart

Index: lib/src/chain.dart
diff --git a/lib/src/chain.dart b/lib/src/chain.dart
index 2e63ef02c6ffb3652a27d8bacb029f3cf2598755..4baec216c8757a5de7f74c4ec3be105636aad78d 100644
--- a/lib/src/chain.dart
+++ b/lib/src/chain.dart
@@ -14,6 +14,7 @@ import 'trace.dart';
 import 'utils.dart';
 
 /// A function that handles errors in the zone wrapped by [Chain.capture].
+@Deprecated("Will be removed in stack_trace 2.0.0.")
 typedef void ChainHandler(error, Chain chain);
 
 /// A chain of stack traces.
@@ -63,7 +64,7 @@ class Chain implements StackTrace {
   /// considered unhandled.
   ///
   /// If [callback] returns a value, it will be returned by [capture] as well.
-  static capture(callback(), {ChainHandler onError}) {
+  static capture(callback(), {void onError(error, Chain chain)}) {
     var spec = new StackZoneSpecification(onError);
     return runZoned(() {
       try {