Add a comment about counter availability in M45 branch
Add a comment about counter availability in M45 branch

R=jochen@chromium.org
NOTRY=true

Review URL: https://codereview.chromium.org/1235963004

git-svn-id: bf5cd6ccde378db821296732a091cfbcf5285fbd@198954 bbb929c8-8fbe-4397-9dbb-9b2b20218538

Pluto-tv/blink-crosswalk,Pluto-tv/blink-crosswalk,Pluto-tv/blink-crosswalk,Pluto-tv/blink-crosswalk,Pluto-tv/blink-crosswalk,Pluto-tv/blink-crosswalk,Pluto-tv/blink-crosswalk,Pluto-tv/blink-crosswalk,Pluto-tv/blink-crosswalk,Pluto-tv/blink-crosswalk