Add GC events to transitions perf test for gallery (#84956)

dev/integration_tests/flutter_gallery/test_driver/transitions_perf_test.dart

@@ -196,6 +196,7 @@ void main([List<String> args = const <String>[]]) {
         streams: const <TimelineStream>[
           TimelineStream.dart,
           TimelineStream.embedder,
+          TimelineStream.gc,
         ],
       );