Return the userChoice promise from beforeinstallpromptevent.prompt().

This corrects a spec violation in the implementation of
beforeinstallpromptevent, where the prompt() method was not returning
the event's userChoice promise. Web tests are updated to test this.


Change-Id: I6e1bd2f83a287d4e7888a873984760bdecab0161
Commit-Queue: Mounir Lamouri <>
Auto-Submit: Dominick Ng <>
Reviewed-by: Mounir Lamouri <>
Cr-Commit-Position: refs/heads/master@{#662659}
2 files changed