Code review comment for lp:~robertcarr/mir/client-focus-notifications

Summary:

1. Build failure:
test_client_focus_notification.cpp:125:13: error: missing initializer for member ‘MirSurfaceParameters::output_id’ [-Werror=missing-field-initializers]
             };
             ^

2. _enum_max_ is not accurate. It's not the max value but is in fact one past the max value. Hence the existing _arraysize_ is more appropriate.

3. mir_surface_attrib_focus should not exist; focus is not a per-surface attribute. For reasons I have mentioned several times since June. Focus is per input device (for non-pointing devices: keyboard, voice...). Though could probably be simplified to one focus per session. Something like: SurfaceID Session::focussed_surface() const;