message: Enable cross-signing lab when key in storage
  When we're starting a new session and find the cross-signing keys in secret
  storage, auto-enable the lab for the new session.
  Fixes
diff: @@ -1834,6 +1834,7 @@ export default createReactClass({
  this._accountPassword = null;
  this._accountPasswordTimer = null;
  }, 60 * 5 * 1000);
  +
  // Wait for the client to be logged in (but not started)
  // which is enough to ask the server about account data.
  const loggedIn = new Promise(resolve => {
  @@ -1867,6 +1868,9 @@ export default createReactClass({
  }
  if (masterKeyInStorage) {
  + // Auto-enable cross-signing for the new session when key found in
  + // secret storage.
  + SettingsStore.setFeatureEnabled("feature_cross_signing", true);
  this.setStateForNewView({ view: VIEWS.COMPLETE_SECURITY });
  } else if (SettingsStore.isFeatureEnabled("feature_cross_signing")) {
  // This will only work if the feature is set to 'enable' in the config,
  