Fix the download_links and download_filename_controller example extensions.

Host permissions are not necessary for download() but are for executeScript.

Tested on 31.0.1650 on mac.

R=asargent@chromium.org

Review URL: https://codereview.chromium.org/27516009

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@229227 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 229227