Fix unexpected behavior when hitting enter in factory_Audio test

BUG=chrome-os-partner:6074
TEST=None

Change-Id: I46f1169827d5e78fe7bc6c7f61ba4c82ea756f5d
Reviewed-on: https://gerrit.chromium.org/gerrit/11348
Reviewed-by: Rong Chang <rongchang@chromium.org>
Commit-Ready: Hsinyu Chao <hychao@chromium.org>
Tested-by: Hsinyu Chao <hychao@chromium.org>
diff --git a/client/site_tests/factory_Audio/factory_Audio.py b/client/site_tests/factory_Audio/factory_Audio.py
index 2feec33..b31ce7f 100644
--- a/client/site_tests/factory_Audio/factory_Audio.py
+++ b/client/site_tests/factory_Audio/factory_Audio.py
@@ -124,6 +124,10 @@
         return True
 
     def key_release_callback(self, widget, event):
+        # Make sure we capture more advanced key events only when
+        # entered a subtest.
+        if self._subtest_widget is None:
+            return True
         name = self._current_sample
         if event.keyval == gtk.keysyms.Tab:
             self._status_map[name] = ful.FAILED