ended attribute has been deprecated. Adding usecounter to gather current usage statistics and let users know that this attribute may be removed in the future and will be replaced with active attribute

BUG=392785

New Spec= http://dev.w3.org/2011/webrtc/editor/getusermedia.html#mediastream
Old Spec= http://dev.w3.org/2011/webrtc/editor/archives/20130824/getusermedia.html#mediastream

Review URL: https://codereview.chromium.org/467093003

git-svn-id: svn://svn.chromium.org/blink/trunk@181297 bbb929c8-8fbe-4397-9dbb-9b2b20218538