Apply default wallpaper from customization manifest.

ash/desktop_background/wallpaper_resizer.cc

Index: ash/desktop_background/wallpaper_resizer.cc
diff --git a/ash/desktop_background/wallpaper_resizer.cc b/ash/desktop_background/wallpaper_resizer.cc
index 46497b2c1c84b6b45a7d36c0acbdee4e7dfd540e..7ab4ac429c76d4d66521f6d14a2f878b85fae258 100644
--- a/ash/desktop_background/wallpaper_resizer.cc
+++ b/ash/desktop_background/wallpaper_resizer.cc
@@ -84,6 +84,9 @@ void Resize(SkBitmap orig_bitmap,
               sub_image, skia::ImageOperations::RESIZE_LANCZOS3,
               new_width, new_height);
         }
+        break;
+      case WALLPAPER_LAYOUT_UNKNOWN:
+        NOTREACHED();
     }
   }
 
@@ -93,8 +96,6 @@ void Resize(SkBitmap orig_bitmap,
 
 }  // namespace
 
-const int kInvalidResourceID = -1;
-
 // static
 uint32_t WallpaperResizer::GetImageId(const gfx::ImageSkia& image) {
   const gfx::ImageSkiaRep& image_rep = image.GetRepresentation(1.0f);