Fix status area accessability issues.

Fix status area accessability issues.

See BUG for description of issues addressed here.
Primarily this moves a bunch of code from SystemTray inot TrayBackgroundView so that it can be shared by WebNotificationTray, but there is a bit of cleanup and a few bug fixes as well, primarily with how the tray view is hilighted, the child ordering of the trays (so that the system tray is first and thus initially focused), and correctly preventing the launcher from auto-hiding.

BUG=142506

[stevenjb, 2012-08-15 16:46:48]

Ping? (This is ready for review)

[sadrul, 2012-08-15 16:47:01]

Refactoring is best done in separate CLs.

http://codereview.chromium.org/10836227/diff/1/ash/system/status_area_widget.cc
File ash/system/status_area_widget.cc (right):

http://codereview.chromium.org/10836227/diff/1/ash/system/status_area_widget....
ash/system/status_area_widget.cc:308: system_tray_->CreateItems();
Maybe CreateItems can be called from Initialize now?

http://codereview.chromium.org/10836227/diff/1/ash/system/status_area_widget....
ash/system/status_area_widget.cc:314:
UpdateAfterLoginStatusChange(system_tray_delegate_->GetUserLoginStatus());
Can system_tray_delegate() be NULL here?

http://codereview.chromium.org/10836227/diff/1/ash/system/tray/system_tray_bu...
File ash/system/tray/system_tray_bubble.cc (right):

http://codereview.chromium.org/10836227/diff/1/ash/system/tray/system_tray_bu...
ash/system/tray/system_tray_bubble.cc:328: tray_->UpdateShouldShowLauncher();
Will this hide the launcher immediately?

[stevenjb, 2012-08-15 21:51:04]

Yeah, sorry for the complex CL, broken into three parts now.

http://codereview.chromium.org/10836227/diff/1/ash/system/status_area_widget.cc
File ash/system/status_area_widget.cc (right):

http://codereview.chromium.org/10836227/diff/1/ash/system/status_area_widget....
ash/system/status_area_widget.cc:308: system_tray_->CreateItems();
On 2012/08/15 16:47:01, sadrul wrote:
> Maybe CreateItems can be called from Initialize now?

Done.

http://codereview.chromium.org/10836227/diff/1/ash/system/status_area_widget....
ash/system/status_area_widget.cc:314:
UpdateAfterLoginStatusChange(system_tray_delegate_->GetUserLoginStatus());
On 2012/08/15 16:47:01, sadrul wrote:
> Can system_tray_delegate() be NULL here?
Looks like not, removed test.

http://codereview.chromium.org/10836227/diff/1/ash/system/tray/system_tray_bu...
File ash/system/tray/system_tray_bubble.cc (right):

http://codereview.chromium.org/10836227/diff/1/ash/system/tray/system_tray_bu...
ash/system/tray/system_tray_bubble.cc:328: tray_->UpdateShouldShowLauncher();
On 2012/08/15 16:47:01, sadrul wrote:
> Will this hide the launcher immediately?

This will trigger a call to
Shell::GetInstance()->shelf()->UpdateAutoHideState();