GitLab

There were corruptions reported on Android where endpoint maps in both
MultiplexRouter and ChannelAssociatedGroupController got null entries in
them. This CL helps to investigate how null entries could sneak into the
maps.

BUG=750267,754946

Change-Id: I787566addc4c56290e0784e202ec15c0fc25af3e
Reviewed-on: https://chromium-review.googlesource.com/666020
Commit-Queue: Yuzhu Shen <yzshen@chromium.org>
Reviewed-by: Ken Rockot <rockot@chromium.org>
Cr-Commit-Position: refs/heads/master@{#501907}