Add two new gallery types to preferences: scan result, and blacklisted scan result.

This types will be used to manage discovered media locations.

BUG=161119

Review URL: https://codereview.chromium.org/131223008

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@244868 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 244868