Hook up v8 use counter API to blink's use counter

BUG=none
R=eseidel@chromium.org

Review URL: https://codereview.chromium.org/346243002

git-svn-id: svn://svn.chromium.org/blink/trunk@176848 bbb929c8-8fbe-4397-9dbb-9b2b20218538