Attempt to get more data from multiple_isolate_list_test

tests/standalone/vmservice/test_helper.dart

 // Copyright (c) 2013, 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.
 
 library vmservice_test_helper;
 
 import 'dart:async';
 import 'dart:io';
 import 'dart:json' as JSON;
 import 'dart:utf' as UTF;
@@ skipping 30 matching lines @@
       onRequestFailed(e);
       return;
     }
     var reply;
     try {
       reply = JSON.parse(replyAsString);
     } catch (e) {
       onRequestFailed(e);
       return;
     }
-    // Received a map.
-    Expect.isTrue(reply is Map);
-    // Has a 'type' key.
-    Expect.isNotNull(reply['type']);
-    onRequestCompleted(reply);
+    if (reply is! Map) {
+        onRequestFailed('Reply was not a map: $reply');
+        return;
+    }
+    if (reply['type'] == null) {
+        onRequestFailed('Reply does not contain a type key: $reply');
+        return;
+    }
+    try {
+        onRequestCompleted(reply);
+    } catch(e) {
+        onRequestFailed('Test callback failed: $e');
+    }
   }
 
   void onRequestFailed(dynamic error) {
     Expect.fail('Failed to make request: $error');
   }
 
   void onRequestCompleted(Map response);
 }
 
 class TestLauncher {
@@ skipping 84 matching lines @@
     var exists = false;
     isolateList['members'].forEach((isolate) {
       if (isolate['id'] == id) {
         exists = true;
         Expect.isTrue(isolate['name'].startsWith(name));
       }
     });
     Expect.isTrue(exists);
   }
 }