Modify WebSocketHandle[Client] interface.

Modify WebSocketHandle and WebSocketHandleClient public interface to address review comments at https://codereview.chromium.org/22815034/.

BUG=275459
R=tyoshino, abarth

Review URL: https://chromiumcodereview.appspot.com/23948002

git-svn-id: svn://svn.chromium.org/blink/trunk@158134 bbb929c8-8fbe-4397-9dbb-9b2b20218538