Move statistics_provider to chromeos/system

BUG=270135
For sync/util/get_session_name.cc (comment change only):
TBR=tim@chromium.org

Review URL: https://codereview.chromium.org/25112004

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@227700 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 227700