GitLab

* Renaming AccountInfo to AccountMapping.
* Adding status and timestamp of it's last change
* Removing last message timestamp, as with introduction of
  message ack event, it is no longer needed

BUG=374969
R=zea@chromium.org

Review URL: https://codereview.chromium.org/443573002

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@287919 0039d316-1c4b-4281-b951-d872f2087c98