ash: Display system background while loading wallpaper.

ash/shell_window_ids.h

 // Copyright (c) 2012 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef ASH_SHELL_WINDOW_IDS_H_
 #define ASH_SHELL_WINDOW_IDS_H_
 
 // Declarations of ids of special shell windows.
 
 namespace ash {
@@ skipping 16 matching lines @@
 // windows (which we want to display while the screen is locked; effectively
 // containers stacked above kShellWindowId_LockSystemModalContainer).  Only used
 // by PowerButtonController for animating lower-level containers.
 const int kShellWindowId_LockScreenRelatedContainersContainer = 2;
 
 // A container used for windows of WINDOW_TYPE_CONTROL that have no parent.
 // This container is not visible.
 const int kShellWindowId_UnparentedControlContainer = 3;
 
 // System level background. Sits beneach the desktop background and is only
-// visible when in a workspace other than the desktop. When switching from the
-// desktop workspace to to another workspace the desktop background scales
-// slightly. This exposes the system level background beneath it.
+// visible when the desktop background has not yet been loaded or a workspace
+// other than the desktop is being displayed. When switching from the desktop
+// workspace to to another workspace the desktop background scales slightly.
+// This exposes the system level background beneath it.
 const int kShellWindowId_SystemBackgroundContainer = 4;
 
 // The desktop background window.
 const int kShellWindowId_DesktopBackgroundContainer = 5;
 
 // TODO(sky): rename kShellWindowId_DefaultContainer when Workspace2 is the
 // default.
 
 // The container for standard top-level windows.
 // WARNING: when Workspace2 is enabled the only children of
@@ skipping 52 matching lines @@
 
 // ID of the window created by PhantomWindowController.
 const int kShellWindowId_PhantomWindow = 22;
 
 }  // namespace internal
 
 }  // namespace ash
 
 
 #endif  // ASH_SHELL_WINDOW_IDS_H_