Add location information to the JSON reporter.

lib/src/runner/remote_listener.dart

Index: lib/src/runner/remote_listener.dart
diff --git a/lib/src/runner/remote_listener.dart b/lib/src/runner/remote_listener.dart
index a041ccd35eb668d4c45f48eec3785d085746b496..b368783210aec0182e90a7b0697c58ea9bbf44e8 100644
--- a/lib/src/runner/remote_listener.dart
+++ b/lib/src/runner/remote_listener.dart
@@ -125,6 +125,7 @@ class RemoteListener {
       "type": "group",
       "name": group.name,
       "metadata": group.metadata.serialize(),
+      "trace": group.trace?.toString(),
       "setUpAll": _serializeTest(channel, group.setUpAll, parents),
       "tearDownAll": _serializeTest(channel, group.tearDownAll, parents),
       "entries": group.entries.map((entry) {
@@ -154,6 +155,7 @@ class RemoteListener {
       "type": "test",
       "name": test.name,
       "metadata": test.metadata.serialize(),
+      "trace": test.trace?.toString(),
       "channel": testChannel.id
     };
   }