ash: Display system background while loading wallpaper.

ash/wm/workspace/system_background_controller.h

Index: ash/wm/workspace/system_background_controller.h
diff --git a/ash/wm/workspace/system_background_controller.h b/ash/wm/workspace/system_background_controller.h
index ca78ab8decfe434933f975ce7fa224d7535981eb..4b84fc08ba2a9541f03f4bacc183afc005f33f8a 100644
--- a/ash/wm/workspace/system_background_controller.h
+++ b/ash/wm/workspace/system_background_controller.h
@@ -8,6 +8,8 @@
 #include "ash/ash_export.h"
 #include "base/basictypes.h"
 
+typedef unsigned int SkColor;
+
 namespace aura {
 class RootWindow;
 };
@@ -20,9 +22,12 @@ namespace internal {
 // level background.
 class ASH_EXPORT SystemBackgroundController {
  public:
-  explicit SystemBackgroundController(aura::RootWindow* root);
+  SystemBackgroundController(aura::RootWindow* root, SkColor color);
   ~SystemBackgroundController();
 
+  // Changes the background color.
+  void SetColor(SkColor color);
+
  private:
   class View;