Make PendingReceiverState and ConnectionGroup::Ref move constructor/assign operator noexcept.

Compilation was failing because PendingReceiver had declared its move
constructor and assign operators as noexcept with default implementation. But
its member PendingReceiverState, and ConnectionGroup::Ref, as member of
PendingReceiverState, did no declare them as noexcept.

Bug: 819294
Change-Id: I6dcab6cddfbffcdb069551c042124dd2988f8a78
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1708142
Commit-Queue: José Dapena Paz <jose.dapena@lge.com>
Reviewed-by: Scott Violet <sky@chromium.org>
Cr-Commit-Position: refs/heads/master@{#679112}