The callback will be called when a lock topic changes its lock
state.
Possible states are:
“unlocked” - nobody holds the wake lock.
“locked-foreground” - at least one window holds the wake lock,
and it is visible.
“locked-background” - at least one window holds the wake lock,
but all of them are hidden.
| aTopic | The resource name related to the wake lock. |
| aState | The wake lock state |