Some callback wrappers set the callback_ member at the start, but
most set it after calling any owned implementation of Start().
Setting it after the call means that the callback_ is not set up
for any callbacks that happen during the call.
This cl fixes that by setting the callback_ member before any
calls are made in Start().
Bug: chromium:916961
Change-Id: Id26f8cc98377ef217f928095834162f5526c1fdf
Reviewed-on: https://webrtc-review.googlesource.com/c/117040
Reviewed-by: Brave Yao <braveyao@webrtc.org>
Commit-Queue: Gary Kacmarcik <garykac@chromium.org>
Cr-Commit-Position: refs/heads/master@{#26231}
2bb29f018a