Add a "when" parameter to Chain.capture().

test/chain/chain_test.dart

 // Copyright (c) 2015, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 import 'dart:async';
 
 import 'package:path/path.dart' as p;
 import 'package:stack_trace/stack_trace.dart';
 import 'package:test/test.dart';
 
@@ skipping 18 matching lines @@
       var chain = new Chain.parse(
           '===== asynchronous gap ===========================\n'
           '===== asynchronous gap ===========================\n');
       expect(chain.traces, hasLength(3));
       expect(chain.traces[0].frames, isEmpty);
       expect(chain.traces[1].frames, isEmpty);
       expect(chain.traces[2].frames, isEmpty);
     });
   });
 
+  group("Chain.capture() with when: false", () {
+    test("with no onError doesn't block errors", () {
+      expect(Chain.capture(() => new Future.error("oh no"), when: false),
+          throwsA("oh no"));
+    });
+
+    test("with onError blocks errors", () {
+      Chain.capture(() {
+        return new Future.error("oh no");
+      }, onError: expectAsync((error, chain) {
+        expect(error, equals("oh no"));
+        expect(chain, new isInstanceOf<Chain>());
+      }), when: false);
+    });
+  });
+
   test("toString() ensures that all traces are aligned", () {
     var chain = new Chain([
       new Trace.parse('short 10:11  Foo.bar\n'),
       new Trace.parse('loooooooooooong 10:11  Zop.zoop')
     ]);
 
     expect(chain.toString(), equals(
         'short 10:11            Foo.bar\n'
         '===== asynchronous gap ===========================\n'
         'loooooooooooong 10:11  Zop.zoop\n'));
@@ skipping 238 matching lines @@
         controller = new StreamController()..addError('error', trace);
         expect(Chain.track(controller.stream).toList()
             .catchError((e, stackTrace) {
           expect(e, equals('error'));
           expect(stackTrace.toString(), equals(trace.toString()));
         }), completes);
       });
     });
   });
 }