Add information that some data may not get deleted

BUG=137412

Review URL: https://codereview.chromium.org/108273002

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@241079 0039d316-1c4b-4281-b951-d872f2087c98
Add ClientCertStoreChromeOS which only returns the certs for a given user.

BUG=302125

Review URL: https://codereview.chromium.org/112533002

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@241080 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 241080