cros: Change wallpaper decoding format to default

This issue did not show up earlier because the old wallpaper picker
only contained jpeg images.

Also changes |shrink_to_fit| to true.

Bug: 852844
Change-Id: Ia26a091ee38a6de43454eda0243ff24386e77da8
Reviewed-on: https://chromium-review.googlesource.com/1101400Reviewed-by: Weidong Guo <weidongg@chromium.org>
Commit-Queue: Wenzhao (Colin) Zang <wzang@chromium.org>
Cr-Commit-Position: refs/heads/master@{#567435}

ash/wallpaper/wallpaper_utils/wallpaper_decoder.cc

@@ -40,8 +40,8 @@ void DecodeWallpaper(const std::string& image_data,
   std::vector<uint8_t> image_bytes(image_data.begin(), image_data.end());
   data_decoder::DecodeImage(
       Shell::Get()->shell_delegate()->GetShellConnector(),
-      std::move(image_bytes), data_decoder::mojom::ImageCodec::ROBUST_JPEG,
-      false /* shrink_to_fit */, kMaxImageSizeInBytes,
+      std::move(image_bytes), data_decoder::mojom::ImageCodec::DEFAULT,
+      true /* shrink_to_fit */, kMaxImageSizeInBytes,
       gfx::Size() /* desired_image_frame_size */,
       base::BindOnce(&ConvertToImageSkia, std::move(callback)));
 }