Clean up some ifdefs around Win Aura.

BUG=330735
R=scottmg@chromium.org, sky@chromium.org

Review URL: https://codereview.chromium.org/136643006

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@248742 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 248742