Fix visitor

```
external/libcxx/include/variant:587:19: error: static assertion failed due to requirement 'is_invocable_v<(anonymous namespace)::Visitor<(lambda at external/libchrome-gestures/src/activity_log.cc:310:7), (lambda at external/libchrome-gestures/src/activity_log.cc:314:7), (lambda at external/libchrome-gestures/src/activity_log.cc:318:7), (lambda at external/libchrome-gestures/src/activity_log.cc:322:7), (lambda at external/libchrome-gestures/src/activity_log.cc:326:7)>, const unsigned char &>': `std::visit` requires the visitor to be exhaustive.
  587 |     static_assert(is_invocable_v<_Visitor, _Values...>,

```

Change-Id: Idc9df90d9ca653c241e42818c5a80857ed945730