Fixed alignment issue in tray in guest mode.

In guest mode, the avatar in the system tray is replaced by a label. The label has a variable size vs the fixed height of avatar images. This causes the tray container to shrink resulting in alignment issues.

I've modified the border around the label so that the height of a |TrayUser| will be consistent. I've also add a unit test to enforce this.

BUG=340673
TEST=Current unit tests pass. New unit test passes. Verify bug 340673.

Review URL: https://codereview.chromium.org/189193003

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@256726 0039d316-1c4b-4281-b951-d872f2087c98
Add some VLOG(1)s to ash::DesktopBackgroundController.

I've had to forward-port this patch enough times now to debug
wallpaper issues that I figure it's best to just clean it up
and commit it.

BUG=none

Review URL: https://codereview.chromium.org/103113003

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@256727 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 256726
SVN changes up to revision 256727