Add UMA stats for discarded tabs on a per logged in user base

Each discarded tab will be "stored" in the bucket for the number of users logged in at the time of the occurrence. 
To get to a useful number, the value needs to be normalized by dividing the absolute value per bucket by the corresponding UsersPerSession bucket (in percent).

BUG=321739
TEST=visual

Review URL: https://codereview.chromium.org/104713003

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@239023 0039d316-1c4b-4281-b951-d872f2087c98
Avoid calling blocking and thread unsafe functions in
NetworkChangeNotifierWin::GetCurrentConnectionType().

BUG=324913,118524

Review URL: https://codereview.chromium.org/105233003

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@239024 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 239024