ChromeOS: Fix DCHECK hit when logging under Guest

ChromeOS: Fix DCHECK hit when logging under Guest

We should not SwitchToLastActiveUser() when there is only one user logged in.
This covers restart on signin, when last_active_user may be outdated.

BUG=714250
Review-Url: https://codereview.chromium.org/2872133009
Cr-Commit-Position: refs/heads/master@{#471127}
Committed: https://chromium.googlesource.com/chromium/src/+/67cd35cee72cda91bc0f8254b1efc080e737d848

[Alexander Alekseev, 2017-05-11 20:09:13]

alemate@chromium.org changed reviewers:
+ xiyuan@chromium.org

[Alexander Alekseev, 2017-05-11 20:09:13]

Please review.

[Alexander Alekseev, 2017-05-11 20:09:36]

The CQ bit was checked by alemate@chromium.org to run a CQ dry run

[commit-bot: I haz the power, 2017-05-11 20:10:35]

Dry run: CQ is trying da patch.

Follow status at:
https://chromium-cq-status.appspot.com/v2/patch-status/codereview.chromium.or...

[xiyuan, 2017-05-11 20:15:18]

lgtm

[commit-bot: I haz the power, 2017-05-11 21:54:52]

The CQ bit was unchecked by commit-bot@chromium.org

[commit-bot: I haz the power, 2017-05-11 21:54:53]

Dry run: This issue passed the CQ dry run.

[Alexander Alekseev, 2017-05-11 23:34:37]

The CQ bit was checked by alemate@chromium.org

[commit-bot: I haz the power, 2017-05-11 23:35:56]

CQ is trying da patch.

Follow status at:
https://chromium-cq-status.appspot.com/v2/patch-status/codereview.chromium.or...

[commit-bot: I haz the power, 2017-05-11 23:56:11]

CQ is committing da patch.

Bot data: {"patchset_id": 1, "attempt_start_ts": 1494545677229050, "parent_rev":
"2e6f9e37552719be81e028ca927d16c4dca681fc", "commit_rev":
"67cd35cee72cda91bc0f8254b1efc080e737d848"}

[commit-bot: I haz the power, 2017-05-11 23:56:21]

Description was changed from

==========
ChromeOS: Fix DCHECK hit when logging under Guest

We should not SwitchToLastActiveUser() when there is only one user logged in.
This covers restart on signin, when last_active_user may be outdated.

BUG=714250
==========

to

==========
ChromeOS: Fix DCHECK hit when logging under Guest

We should not SwitchToLastActiveUser() when there is only one user logged in.
This covers restart on signin, when last_active_user may be outdated.

BUG=714250

Review-Url: https://codereview.chromium.org/2872133009
Cr-Commit-Position: refs/heads/master@{#471127}
Committed:
https://chromium.googlesource.com/chromium/src/+/67cd35cee72cda91bc0f8254b1ef...
==========

[commit-bot: I haz the power, 2017-05-11 23:56:22]

Committed patchset #1 (id:1) as
https://chromium.googlesource.com/chromium/src/+/67cd35cee72cda91bc0f8254b1ef...