cros: Fix missing windows/launcher after resume/screen unlock

cros: Fix missing windows/launcher after resume/screen unlock

When the screen is locked the desktop wallpaper background widget is pulled
"forward" to hide the user's browser windows and the launcher.  There is a
race condition between a window animation triggered by wallpaper reloading at
device resume and code in screen unlock that "pushes" the background back
behind the launcher and browsers.  There can temporarily be two backgrounds
and we need to move them both to the back.  The extra one will be cleaned up
when the animation completes.

See bug for details on the race.

I'm working on unit tests for this, but that will require some refactoring
and I wanted to keep this patch simple for backport to R23.

BUG=149043
TEST=interactive_ui_tests ScreenLocker.*, set option to require password on resume, sleep device (close lid or wait for timeout), resume device, verify you can unlock screen with password

Committed: https://src.chromium.org/viewvc/chrome?view=rev&revision=159954

[James Cook, 2012-10-03 17:15:40]

Biao, PTAL.  This fixes the repro case you found yesterday (I verified on the
device).  I removed my CHECK from ScreenLocker since I don't think it's
necessary any more and I don't want to crash if for some reason we temporarily
have no widgets to move.

[bshe, 2012-10-03 17:21:49]

Thanks for fixing it.
lgtm

On 2012/10/03 17:15:40, James Cook (Chromium) wrote:
> Biao, PTAL.  This fixes the repro case you found yesterday (I verified on the
> device).  I removed my CHECK from ScreenLocker since I don't think it's
> necessary any more and I don't want to crash if for some reason we temporarily
> have no widgets to move.

[James Cook, 2012-10-03 17:36:18]

Dave, can I get OWNERs approval for my change to 	
chrome/browser/chromeos/login/screen_locker.cc?  I'm just removing a CHECK
that's no longer necessary (and a WARNING I accidentally left in a previous
commit).

[DaveMoore, 2012-10-03 19:49:28]

lgtm