function getBroadcast(callback) {
  socket.on('broadcastEvents', (entries) => {
    entries.forEach((entry) => {
      entry.events = entry.events.map((entry) => {
        return Blockly.Events.fromJson(entry, Blockly.getMainWorkspace());
      });
    });
    callback(entries);
  });
}
Listen for events broadcast by the server.
@param {!Function} callback The callback handler that passes the events to
the workspace.
@returns {!Promise} Promise object that represents the success of the write.
@public