Increase Web Bluetooth device scanning duration

This CL increases the Web Bluetooth device scanning duration from 10
seconds to 60 seconds. Also added UMA for the event that the re-scan
link is pressed and the duration to find at lease one Bluetooth device.

BUG=419413

Review-Url: https://codereview.chromium.org/2506163002
Cr-Commit-Position: refs/heads/master@{#433074}
4 files changed