Grant time-based user activation from extension events that grant a user gesture

[oliverdunk]

In event listeners like action.onClicked, we grant a user gesture. This allows extension developers to call other APIs that have a user gesture requirement.

There is a lack of consistency around if this is granted just while the callback runs or for an extended time period. For example, Chrome currently only grants the gesture while the listener is running, preventing the use of asynchronous code before calling an API that needs the user gesture.

We should use the concept of User Activation consistently where any user gesture granted by the extensions system grants the gesture for a browser defined time-period.

[tophf]

Sounds like transient activation in the web platform so aligning with it seems sensible. There's also navigator.userActivation API.