[reland] Do not set default wallpaper unless it should do so.

TBR=bshe@chromium.org, alemate@chromium.org

Bug: 751382
Change-Id: Id0793dfe467f737526a95b1e66ed01fbb8860bda
Reviewed-on: https://chromium-review.googlesource.com/619754
Commit-Queue: Xiaoqian Dai <xdai@chromium.org>
Reviewed-by: Alexander Alekseev <alemate@chromium.org>
Reviewed-by: Biao She <bshe@chromium.org>
Cr-Original-Commit-Position: refs/heads/master@{#498325}
Reviewed-on: https://chromium-review.googlesource.com/646430
Cr-Commit-Position: refs/heads/master@{#498982}
void WallpaperManager::OnPolicyFetched(const std::string& policy,
                                       const AccountId& account_id,
                                       std::unique_ptr<std::string> data) {
  if (!data)
    return;

  user_image_loader::StartWithData(
      task_runner_, std::move(data), ImageDecoder::ROBUST_JPEG_CODEC,
      0,  // Do not crop.
      base::Bind(&WallpaperManager::SetPolicyControlledWallpaper,
                 weak_factory_.GetWeakPtr(), account_id));
}

void WallpaperManager::OnPolicyFetched(const std::string& policy,
                                       const AccountId& account_id,
                                       std::unique_ptr<std::string> data) {
  if (!data)
    return;

  user_image_loader::StartWithData(
      task_runner_, std::move(data), ImageDecoder::ROBUST_JPEG_CODEC,
      0,  // Do not crop.
      base::Bind(&WallpaperManager::SetPolicyControlledWallpaper,
                 weak_factory_.GetWeakPtr(), account_id));
}
