Fixed by revert: https://chromium-review.googlesource.com/c/chromium/src/+/1354327

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/79aa0156b8fabb6a7baf0c50196ecd3af14ecf08

commit 79aa0156b8fabb6a7baf0c50196ecd3af14ecf08
Author: Kyle Horimoto <khorimoto@chromium.org>
Date: Wed Nov 28 23:37:37 2018

[CrOS MultiDevice] Re-land crash fix for BleConnectionManagerImpl.

Originally landed as:
https://chromium-review.googlesource.com/c/1352855
Reverted as:
https://chromium-review.googlesource.com/c/chromium/src/+/1354327

First patch set includes original CL, and subsequent patches contain
updates to fix the failing test.

Original CL descrition:

When a SecureChannel disconnects due to authentication failures,
BleConnectionManagerImpl invokes the relevant failure callback, which
then causes ConnectionAttemptBase to cancel the connection attempt.

When the attempt is cancelled, the SecureChannel object is deleted via
BleConnectionManagerImpl::ProcessPotentialLingeringChannel(), but
BleConnectionManagerImpl::HandleSecureChannelDisconnection() assumed
that the object was still valid and tried to to remove itself as an
observer, causing a segfault.

The fix is to check whether the object has been deleted before
attempting to call RemoveObserver().

Bug: 905904,  909883 
Change-Id: I770bff8f05865aeac8b7513d7193d0b7a40d056e
Reviewed-on: https://chromium-review.googlesource.com/c/1354333
Reviewed-by: Ryan Hansberry <hansberry@chromium.org>
Commit-Queue: Kyle Horimoto <khorimoto@chromium.org>
Cr-Commit-Position: refs/heads/master@{#611937}
[modify] https://crrev.com/79aa0156b8fabb6a7baf0c50196ecd3af14ecf08/chromeos/services/secure_channel/ble_connection_manager_impl.cc
[modify] https://crrev.com/79aa0156b8fabb6a7baf0c50196ecd3af14ecf08/chromeos/services/secure_channel/ble_connection_manager_impl_unittest.cc