This event is emitted after a layer's location property has changed value.
This event is also emitted when a layer without visible history
has reached a new location. If you are only interested in changes the are visible in
the browser's address bar, observe up:location:changed
instead.
The event is also event for location changes on the root layer.
This event is not emitted when an overlay is opened. For this observe up:layer:opened
instead.
The current layer location.