Notify WebSocket connection failure, Blink side

In order to set |wasClean| property of CloseEvent and show the failure message
correctly, The blink-side WebSocket need to know whether the connection
is dropped because of a server request.

chromium side change is: https://codereview.chromium.org/34753008/

BUG=310405

Review URL: https://codereview.chromium.org/36033003

git-svn-id: svn://svn.chromium.org/blink/trunk@161135 bbb929c8-8fbe-4397-9dbb-9b2b20218538