The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/7dbdaebce5372443a810ad0c643ea17718607946

commit 7dbdaebce5372443a810ad0c643ea17718607946
Author: Scott Violet <sky@chromium.org>
Date: Tue Dec 11 22:39:02 2018

chromeos: ensure there is active window when unblocking

SessionController may block windows (such as browser windows) from becoming
active. When trasitioning from blocking to not-blocking we should ensure there
is an active window. To do otherwise means there may be no active window,
which is a state we try to ensure doesn't exist.

BUG= 914017 
TEST=covered by tests

Change-Id: I5d9392ea7706ea3603ecc6f68201f4931ebfe642
Reviewed-on: https://chromium-review.googlesource.com/c/1372408
Reviewed-by: Xiyuan Xia <xiyuan@chromium.org>
Commit-Queue: Scott Violet <sky@chromium.org>
Cr-Commit-Position: refs/heads/master@{#615700}
[modify] https://crrev.com/7dbdaebce5372443a810ad0c643ea17718607946/ash/session/session_controller.cc
[modify] https://crrev.com/7dbdaebce5372443a810ad0c643ea17718607946/ash/session/session_controller.h
[modify] https://crrev.com/7dbdaebce5372443a810ad0c643ea17718607946/ash/session/session_controller_unittest.cc
[modify] https://crrev.com/7dbdaebce5372443a810ad0c643ea17718607946/ash/shell.cc
[modify] https://crrev.com/7dbdaebce5372443a810ad0c643ea17718607946/ash/shell.h