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

ash/accelerators/accelerator_controller.cc

Index: ash/accelerators/accelerator_controller.cc
diff --git a/ash/accelerators/accelerator_controller.cc b/ash/accelerators/accelerator_controller.cc
index b3435d3333d5febf7b6b7c8382545f45c59f0a50..1c3da9ff18edd2d43e9c64e1438bec19b3995f4f 100644
--- a/ash/accelerators/accelerator_controller.cc
+++ b/ash/accelerators/accelerator_controller.cc
@@ -159,10 +159,11 @@ bool HandleToggleDesktopBackgroundMode() {
       Shell::GetInstance()->desktop_background_controller();
   if (desktop_background_controller->desktop_background_mode() ==
       DesktopBackgroundController::BACKGROUND_IMAGE) {
-    desktop_background_controller->SetDesktopBackgroundSolidColorMode();
+    desktop_background_controller->SetDesktopBackgroundSolidColorMode(
+        SK_ColorBLACK);
   } else {
-    Shell::GetInstance()->user_wallpaper_delegate()->
-        SetLoggedInUserWallpaper();
+    ash::Shell::GetInstance()->user_wallpaper_delegate()->
+        InitializeWallpaper();
   }
   return true;
 }