Sanitize counter names and fix a division error in counter totals

BUG=335692
TBR=tonyg

Review URL: https://codereview.chromium.org/142163002

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@245722 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 245722