Use CompletionOnceCallback in struct WaitingForRead.

Since CompletionOnceCallback is non-copyable, therefore WaitingForRead
becomes non-copyable.  This Cl adds a move constructor so that
WaitingForRead can be put in a std::map.

Bug: 807724
Change-Id: I57dce65d46626ce0c39cd3e2e738ad9d6979165c
Reviewed-on: https://chromium-review.googlesource.com/1156862
Reviewed-by: Ryan Hamilton <rch@chromium.org>
Commit-Queue: Bence Béky <bnc@chromium.org>
Cr-Commit-Position: refs/heads/master@{#579961}
2 files changed