* Electron version: 1.6.10
* Operating system: macOS Sierra 10.12.4 (16E195)

# Improve Handoff API support

Hi!

Today the API of Handoff provides the methods: `setUserActivity`, `getCurrentActivityType` and dispatch the event `continue-activity`

I'm using Handoff and noticed that in some circumstances the broadcast takes a long time to update its userInfo which does not happen on the native iOS client

1. To invalidate or resign the current activity we currently need to create a non-existing activity type and set it as the current activity. There's no way to handle the activity life cycle through electron.
2. When we need to update a given user activity userInfo frequently (i.e in response to a search bar's text changes), we have no efficient way. Setting a new userActivity with the updated information takes several seconds to bridge, whereas doing this on iOS native app is instantaneous.

I believe that exposing a bit more of the NSUserActivity API to Electron would help, namely `becomeCurrent`, `resignCurrent` and `invalidate` which would address point 1, and `needsSave` and a new event to allow updating an activity when needed to address point 2.
These are described in more detail in https://developer.apple.com/reference/foundation/nsuseractivity.

I'm are open to help in any way i can such as explaining how the native API work, providing sample code or testing possible implementations

Thank you!
atom/browser/api/atom_api_app.cc
else if (name == "music")
    return chrome::DIR_USER_MUSIC;
  else if (name == "pictures")
    return chrome::DIR_USER_PICTURES;
  else if (name == "videos")
    return chrome::DIR_USER_VIDEOS;
  else if (name == "pepperFlashSystemPlugin")
    return chrome::FILE_PEPPER_FLASH_SYSTEM_PLUGIN;
  else
    return -1;
}
bool NotificationCallbackWrapper(
    const base::RepeatingCallback<
        void(const base::CommandLine::StringVector& command_line,
             const base::FilePath& current_directory)>& callback,
    const base::CommandLine::StringVector& cmd,
    const base::FilePath& cwd) {
  
  if (Browser::Get()->is_ready()) {
    callback.Run(cmd, cwd);
  } else {
    scoped_refptr<base::SingleThreadTaskRunner> task_runner(
        base::ThreadTaskRunnerHandle::Get());
    task_runner->PostTask(
        FROM_HERE, base::BindOnce(base::IgnoreResult(callback), cmd, cwd));
  }
  
  return !Browser::Get()->is_shutting_down();
}
void GotPrivateKey(std::shared_ptr<content::ClientCertificateDelegate> delegate,