This also removes incognito_separator.png, which can be replaced with a
solid-color View.

BUG=289843
R=aurimas@chromium.org, tedchoc@chromium.org

Review URL: https://codereview.chromium.org/339293002

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@278120 0039d316-1c4b-4281-b951-d872f2087c98