Improvements to causal async stack traces

runtime/observatory/tests/service/test_helper.dart

Index: runtime/observatory/tests/service/test_helper.dart
diff --git a/runtime/observatory/tests/service/test_helper.dart b/runtime/observatory/tests/service/test_helper.dart
index e1f43af87aaf206766376a74a43ca944456440b5..734d14de97970b408b0885a86a2c4e74c8005ed5 100644
--- a/runtime/observatory/tests/service/test_helper.dart
+++ b/runtime/observatory/tests/service/test_helper.dart
@@ -8,7 +8,6 @@ import 'dart:async';
 import 'dart:convert';
 import 'dart:io';
 import 'package:observatory/service_io.dart';
-import 'package:stack_trace/stack_trace.dart';
 import 'service_test_common.dart';
 
 /// Will be set to the http address of the VM's service protocol before
@@ -294,7 +293,7 @@ class _ServiceTesterRunner {
       }
       setupAddresses(serverAddress);
       var name = Platform.script.pathSegments.last;
-      Chain.capture(() async {
+      try {
         var vm =
             new WebSocketVM(new WebSocketVMTarget(serviceWebsocketAddress));
         print('Loading VM...');
@@ -329,16 +328,16 @@ class _ServiceTesterRunner {
         print('All service tests completed successfully.');
         testsDone = true;
         await process.requestExit();
-      }, onError: (error, stackTrace) {
+      } catch (error, stackTrace) {
         if (testsDone) {
           print('Ignoring late exception during process exit:\n'
                 '$error\n#stackTrace');
         } else {
           process.requestExit();
           print('Unexpected exception in service tests: $error\n$stackTrace');
-          throw error;
+          rethrow;
         }
-      });
+      }
     });
   }