Properly handle errors thrown in [Chain.capture]'s [onError] handler.

pkg/stack_trace/test/chain_test.dart

Index: pkg/stack_trace/test/chain_test.dart
diff --git a/pkg/stack_trace/test/chain_test.dart b/pkg/stack_trace/test/chain_test.dart
index d9915ebf1f9767c21b1c8890bd95471d73730b3f..683544f1d26ad885fbd961db53d2cadf35148cd0 100644
--- a/pkg/stack_trace/test/chain_test.dart
+++ b/pkg/stack_trace/test/chain_test.dart
@@ -107,6 +107,29 @@ void main() {
 
       return completer.future;
     });
+
+    test('and relays them to the parent zone', () {
+      var completer = new Completer();
+
+      runZoned(() {
+        Chain.capture(() {
+          inMicrotask(() => throw 'error');
+        }, onError: (error, chain) {
+          expect(error, equals('error'));
+          expect(chain.traces[1].frames,
+              contains(frameMember(startsWith('inMicrotask'))));
+          throw error;
+        });
+      }, onError: (error, chain) {
+        expect(error, equals('error'));
+        expect(chain, new isInstanceOf<Chain>());
+        expect(chain.traces[1].frames,
+            contains(frameMember(startsWith('inMicrotask'))));
+        completer.complete();
+      });
+
+      return completer.future;
+    });
   });
 
   test('capture() without onError passes exceptions to parent zone', () {