Method handleAction

background_scripts/tab_recency.js:100–108

(action, tabId)

  // - action: "register" or "unregister".
  handleAction(action, tabId) {
    if (action == "register") {
      this.register(tabId);
    } else if (action == "deregister") {
      this.deregister(tabId);
    } else {
      throw new Error(`Unexpected action type: ${action}`);
    }
  }

  register(tabId) {
    this.counter++;