Correctly save Activity's state in saveInstanceState

Prior to this change, saveInstanceState would
call directly to Activity.onSaveInstanceState(),
rather than performSaveInstanceState().
This meant that saveManagdDialogs() was not called,
so Activities running under a LocalActivityManager
do not get their dialogs restored on configuration changes.

Change-Id: Id45110a8716a86958c14f4b1ea5a84c9cdf107f1