Adding persistence of user to serial number mappings to RMQ Store
Adding tests for the new functionality

BUG=284553

Review URL: https://codereview.chromium.org/101413007

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@241995 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 241995