Use a #fefefe solid color wallpaper background before user login for GAIA login flow

ash/desktop_background/desktop_background_resources.h

Index: ash/desktop_background/desktop_background_resources.h
diff --git a/ash/desktop_background/desktop_background_resources.h b/ash/desktop_background/desktop_background_resources.h
index 1de8762a6034512a957b51ccc74112f913a53258..a25afa200bfb10fee06b0623bd60390887e872d6 100644
--- a/ash/desktop_background/desktop_background_resources.h
+++ b/ash/desktop_background/desktop_background_resources.h
@@ -6,6 +6,7 @@
 #define ASH_DESKTOP_BACKGROUND_DESKTOP_BACKGROUND_RESOURCES_H_
 
 #include "ash/ash_export.h"
+#include "third_party/skia/include/core/SkColor.h"
 
 namespace ash {
 
@@ -26,6 +27,9 @@ struct ASH_EXPORT WallpaperInfo {
   const char* website;
 };
 
+const SkColor kLoginWallpaperColor = 0xFEFEFE;
+
+ASH_EXPORT int GetSolidColorIndex();
 ASH_EXPORT int GetInvalidWallpaperIndex();
 ASH_EXPORT int GetDefaultWallpaperIndex();
 ASH_EXPORT int GetGuestWallpaperIndex();