WinAsh: Set wallpaper for debug build

Simple pattern to figure out when transparency is broken

BUG=324103
TBR=jamescook

Review URL: https://codereview.chromium.org/108683004

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@240839 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 240839