Use CompletionOnceCallback in WebSocketStream.

Bug: 807724
Change-Id: I71ddcf48ef586baa4d784a76f3d281988e6c2fc4
Reviewed-on: https://chromium-review.googlesource.com/1128180
Reviewed-by: Adam Rice <ricea@chromium.org>
Commit-Queue: Bence Béky <bnc@chromium.org>
Cr-Commit-Position: refs/heads/master@{#575521}
8 files changed