Revert 232142 "Revert 230138 "Delay wallpaper load by 2 * averag..."

Broke Linux ChromiumOS Builder:
http://build.chromium.org/p/chromium.chromiumos/builders/Linux%20ChromiumOS%20Builder/builds/57984/steps/compile/logs/stdio


> Revert 230138 "Delay wallpaper load by 2 * average wallpaper loa..."
> 
> Reason: regression on zgb/alex/mario resulting in login UI being invisible in certain cases. See http://crbug.com/313019
> 
> > Delay wallpaper load by 2 * average wallpaper load time.
> > 
> > BUG=279102,313019
> > 
> > TEST=manual
> > 
> > Review URL: https://codereview.chromium.org/24625003
> 
> TBR=alemate@chromium.org
> 
> Review URL: https://codereview.chromium.org/54333005

TBR=nkostylev@chromium.org

Review URL: https://codereview.chromium.org/54723003

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@232146 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 232146