Component updater exposes an OnDemandUpdater, which can be programmatically called to initiate an update of a component. The current implementation handles such calls with foreground priorities, meaning that the download and the install of the component happen as fast as possible. 

This is the correct behavior when the call to the OnDemandUpdater is the result of a user interaction. 

However, there are cases in which the user is not involved, and still, we'd like to allow OnDemandUpdater calls, and it is ok if the download or the install occur at background priority.

The request is for the OnDemandUpdater class to expose something like:

// The priority of the on demand update. Calls with |BACKGROUND| priority may
// be queued up but calls with |FOREGROUND| priority may be processed right
// away.
enum class Priority { BACKGROUND = 0, FOREGROUND = 1 };