[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::AddObservers() {
  show_user_name_on_signin_subscription_ =
      CrosSettings::Get()->AddSettingsObserver(
          kAccountsPrefShowUserNamesOnSignIn,
          base::Bind(&WallpaperManager::InitializeRegisteredDeviceWallpaper,
                     weak_factory_.GetWeakPtr()));
  device_wallpaper_image_subscription_ =
      CrosSettings::Get()->AddSettingsObserver(
          kDeviceWallpaperImage,
          base::Bind(&WallpaperManager::OnDeviceWallpaperPolicyChanged,
                     weak_factory_.GetWeakPtr()));
}

void WallpaperManager::AddObservers() {
  show_user_name_on_signin_subscription_ =
      CrosSettings::Get()->AddSettingsObserver(
          kAccountsPrefShowUserNamesOnSignIn,
          base::Bind(&WallpaperManager::InitializeRegisteredDeviceWallpaper,
                     weak_factory_.GetWeakPtr()));
  device_wallpaper_image_subscription_ =
      CrosSettings::Get()->AddSettingsObserver(
          kDeviceWallpaperImage,
          base::Bind(&WallpaperManager::OnDeviceWallpaperPolicyChanged,
                     weak_factory_.GetWeakPtr()));
}
