Adding UMA stats for the type of visiting windows

BUG=318862
TEST=visual

Review URL: https://codereview.chromium.org/93443002

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@238731 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 238731