WebSocket: Refactor WebSocket error reports

[Yuta Kitamura]

Currently, the codes that report WebSocket errors to JavaScript console are scaterred among various places in WebCore. This sounds ad-hoc, and could be improved.

We could add a function to WebSocketChannel (and ThreadableWebSocketChannel, WorkerThreadableWebSocketChannel) that corresponds to "fail the WebSocket connection" algorithm in the WebSocket protocol specification (*1), like:

    class WebSocketChannel
    {
        ...
        void fail(const String& errorMessage); // Log the error to JavaScript console, and do close().
        ...
    };

... and use it in places where we need to "fail the WebSocket connection". I think this change will make the code more readable and easier to track.

(*1) In the WebSocket protocol specification, an algorithm called "fail the WebSocket connection" is defined:

http://tools.ietf.org/html/draft-ietf-hybi-thewebsocketprotocol-00#section-6.1
   Certain algorithms require the user agent to *fail the WebSocket
   connection*.  To do so, the user agent must close the WebSocket
   connection, and may report the problem to the user (which would be
   especially useful for developers).

[Yuta Kitamura]

This is done!