Migrate //chromecast/net to net::CompletionOnceCallback

Replace usage of net::CompletionCallback wherever possible, and remove
custom mock implementations of Socket's Write(), Read() and Connect()
methods, now that they already expect a CompletionOnceCallback.

Bug: 807724
Change-Id: I57c4e46f392ad0c09e4fd7dc7670d425ca4ac24b
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1530879
Reviewed-by: Luke Halliwell <halliwell@chromium.org>
Reviewed-by: Bence Béky <bnc@chromium.org>
Commit-Queue: Mario Sanchez Prada <mario@igalia.com>
Cr-Commit-Position: refs/heads/master@{#643362}
2 files changed