Chrome OS OOBE: Increase startup sound delay and add UMA metric.

This CL increases OOBE startup sound delay to 4 seconds, and adds UMA metric
on it.

Bug: 848485
Change-Id: I5401a2625634315760906789fcd69afe04d2972c
Reviewed-on: https://chromium-review.googlesource.com/1173014
Reviewed-by: Ilya Sherman <isherman@chromium.org>
Reviewed-by: Wenzhao (Colin) Zang <wzang@chromium.org>
Commit-Queue: Alexander Alekseev <alemate@chromium.org>
Cr-Commit-Position: refs/heads/master@{#582866}
2 files changed