message: Add null-guard to support browsers that don't support performance
  Like Tor.
  Fixes
diff: @@ -398,6 +398,9 @@ export default React.createClass({
  },
  startPageChangeTimer() {
  + // Tor doesn't support performance
  + if (!performance || !performance.mark) return null;
  +
  // This shouldn't happen because componentWillUpdate and componentDidUpdate
  // are used.
  if (this._pageChanging) {
  @@ -409,6 +412,9 @@ export default React.createClass({
  },
  stopPageChangeTimer() {
  + // Tor doesn't support performance
  + if (!performance || !performance.mark) return null;
  +
  if (!this._pageChanging) {
  console.warn('MatrixChat.stopPageChangeTimer: timer not started');
  return;
  