Add UseCounter features for Document prefixed fullscreen APIs

Since the unprefixed API isn't event implemented yet removal is nowhere
in sight, but it's still interesting to track these features over time.

BUG=none

Review URL: https://codereview.chromium.org/214873002

git-svn-id: svn://svn.chromium.org/blink/trunk@170270 bbb929c8-8fbe-4397-9dbb-9b2b20218538