Platformize PickUnusedPortOrDie()

Merge internal change: 233326398

R=rch@chromium.org

Change-Id: Ia0222dabcbbd9fc4ec2036fd6adc2a13701370e4
Reviewed-on: https://chromium-review.googlesource.com/c/1462213
Commit-Queue: Ryan Hamilton <rch@chromium.org>
Reviewed-by: Ryan Hamilton <rch@chromium.org>
Cr-Commit-Position: refs/heads/master@{#630778}
7 files changed