Make download shelf themeable.
Make download shelf themeable.

BUG=none
TEST=Install a theme, notice that the download shelf now at least somewhat fits with the new theme.
Review URL: http://codereview.chromium.org/159126

git-svn-id: http://src.chromium.org/svn/trunk/src@21205 4ff67af0-8c30-449e-8e8b-ad334ec8d88c

Former-commit-id: 0adb53f815af649d52c3a296c8fb90d0e11be8f8
meego-tablet-ux/meego-app-browser,meego-tablet-ux/meego-app-browser,meego-tablet-ux/meego-app-browser,meego-tablet-ux/meego-app-browser,meego-tablet-ux/meego-app-browser,meego-tablet-ux/meego-app-browser,meego-tablet-ux/meego-app-browser,meego-tablet-ux/meego-app-browser,meego-tablet-ux/meego-app-browser,meego-tablet-ux/meego-app-browser