Show an error bubble on lock screen when user attaches different base

Makes LockContentsView observe DetachableBaseHandler, and display an
error bubble when it detects that the user has attached a base
different than the one they used last.
The bubble has the same style as the auth error bubble, but is not
supposed to be dismissable by the user (so untrusted user can't remove
the error bubble while the device is unattended).

Updates LoginBubble class to support non-dismissable error bubbles -
introduces kFlagPersistent flag that can be passed to ShowErrorBubble.
If the flag is set, the bubble will not be closed on key, mouse or
gesture events.

BUG=796300

Change-Id: I9723ba61450d03bdedb395462994d0b3546e5db0
Reviewed-on: https://chromium-review.googlesource.com/941726
Reviewed-by: Jacob Dufault <jdufault@chromium.org>
Reviewed-by: Xiyuan Xia <xiyuan@chromium.org>
Commit-Queue: Toni Barzic <tbarzic@chromium.org>
Cr-Commit-Position: refs/heads/master@{#542298}
18 files changed