Active WebSocket should send closing handshake to server on page navigation or page close

Specification URL: http://dev.w3.org/html5/websockets/#garbage-collection

BUG=275280

R=tyoshino

Review URL: https://chromiumcodereview.appspot.com/23201008

git-svn-id: svn://svn.chromium.org/blink/trunk@156381 bbb929c8-8fbe-4397-9dbb-9b2b20218538