Light cleanup of CallbackList.

1. C++11ify a few things.
2. Clarify that the callbacks are RepeatingCallbacks.

BUG=714018

Change-Id: I6f1ffeacbcaee54d70a53803a2082cfb11f98f83
Reviewed-on: https://chromium-review.googlesource.com/979196
Commit-Queue: Avi Drissman <avi@chromium.org>
Reviewed-by: kylechar <kylechar@chromium.org>
Reviewed-by: danakj <danakj@chromium.org>
Cr-Commit-Position: refs/heads/master@{#546688}
1 file changed