The change has a legitimate merge conflict. Try clicking the "Rebase" button in the gerrit UI, or fetching the latest origin/master and rebasing on top of that locally. You'll see that they fail and you'll have to do manual conflict resolution.

This same error would have happened with Rietveld when the CQ process itself failed to rebase and push your change.

Yes, but take a look to Patch set 2 for example:
https://build.chromium.org/p/tryserver.chromium.android/builders/linux_android_rel_ng/builds/294974

There was no conflict there. Instead I got this error, it repeated again in Patch Set 5:

===Running git reset --hard (attempt #1)===
In directory: src
HEAD is now at c190586208cd Add support in the network service for different contexts.
===Succeeded in 0.0 mins===
===Running git fetch https://chromium.googlesource.com/chromium/src refs/changes/17/506017/2 (attempt #1)===
In directory: src
From https://chromium.googlesource.com/chromium/src
 * branch                      refs/changes/17/506017/2 -> FETCH_HEAD
===Succeeded in 0.1 mins===
===Running git checkout FETCH_HEAD (attempt #1)===
In directory: src
Previous HEAD position was c190586208cd... Add support in the network service for different contexts.
HEAD is now at 7ce303bc9787... Use a single benchmark for WebRTC telemetry tests.
===Succeeded in 0.0 mins===
===Rebasing===
===Running git checkout -b tmp/9d40d7edb2d6483591c931d23d5a9f21 (attempt #1)===
In directory: src
Switched to a new branch 'tmp/9d40d7edb2d6483591c931d23d5a9f21'
===Succeeded in 0.0 mins===
===Running git rebase c190586208cdae9ddecfd8d33d5aee3fc7c4dd92 (attempt #1)===
In directory: src
First, rewinding head to replay your work on top of it...
fatal: name consists only of disallowed characters: "
===Failed in 0.0 mins===
===Running git rebase --abort (attempt #1)===
In directory: src
No rebase in progress?

Yes, that was the outage announced on chromium-dev yesterday. It was resolved around Pacific EOB yesterday.