Add a flag to disable infobar popup when accessing media drm credentials

for webapps, this is not needed

BUG=297643

Review URL: https://chromiumcodereview.appspot.com/24323013

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@225123 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 225123