make websocket flush accessible.

app/assets/javascripts/editor/websocket.js.erb

@@ -96,6 +96,13 @@ CommandSocket.prototype.getReadyState = function() {
   return this.websocket.readyState;
 };
 
+/**
+ * Flush the websocket.
+ */
+CommandSocket.prototype.flush = function() {
+  this.websocket.flush();
+};
+
 /**
  * Closes the websocket.
  */