Bug 1083775 - [System] status-bar label is overlapped with icons if the ...

...operator text is long in 2.0
Yes, we need to know when the utility tray is about to open. If we use `utilitytrayshow`, that is triggered at the end of the opening animation, the label is resized too late. That results in the label being animated down, then resized to fit the available space afterwards, which is ugly.
That said, the `this.utilityTrayShown = true;` line is not necessary in `utilitytrayshow`.