Bug 977588 - [Dialer] The Active call screen does not have the option to place calls on hold.

Hi Doug! If I do not recall wrong, the reason it to properly prepare (enabling and disabling the buttons) the call screen in the case the user wants to establish a second call before it is shown. Imagine you already have an ongoing call and you tap on the "place new call" button, type a phone number or select one from a contact, and call that number. If we do not prepare the call screen here with these lines of code and we rely only in the notifications of the events, the user will see the call screen with "put on hold" button enabled (since it was enabled due to the ongoing call), then the statechange event will be notified, the "put on hold" button will be disabled (since there is call being established) and once the call is established, the "put on hold" button will be enabled once again. It is just to avoid this "flickering". Are you fine with the proposed solution? :)