Sends a message to the comObj to invoke the action with the supplied data.
@param {String} actionName Action to call.
@param {JSON} data JSON data to send.
@param {Array} [transfers] Optional list of transfers/ArrayBuffers
function messageHandlerSend(actionName, data, transfers) {
    var message = {
      action: actionName,
      data: data
    };
    this.postMessage(message, transfers);
  }