Further fix get_cpu_profile_timeline_rpc_test.

runtime/observatory/tests/service/get_cpu_profile_timeline_rpc_test.dart

Index: runtime/observatory/tests/service/get_cpu_profile_timeline_rpc_test.dart
diff --git a/runtime/observatory/tests/service/get_cpu_profile_timeline_rpc_test.dart b/runtime/observatory/tests/service/get_cpu_profile_timeline_rpc_test.dart
index 2d2b802d9c080122fb4961b873f9c1e16cb2080c..4a6a88d5ca7519a26826487b2efc30e02854395e 100644
--- a/runtime/observatory/tests/service/get_cpu_profile_timeline_rpc_test.dart
+++ b/runtime/observatory/tests/service/get_cpu_profile_timeline_rpc_test.dart
@@ -48,7 +48,7 @@ var tests = [
       expect(event['pid'], isInt);
       expect(event['tid'], isInt);
       expect(event['ts'], isInt);
-      expect(event['category'], equals("Dart"));
+      expect(event['cat'], equals("Dart"));
       expect(frames.containsKey(event['sf']), isTrue);
     }
   },