* 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
const base::DictionaryValue& options) {
  std::string file_data, cert_path;
  base::string16 password;
  net::ScopedCERTCertificateList imported_certs;
  int rv = -1;
  options.GetString("certificate", &cert_path);
  options.GetString("password", &password);
  if (!cert_path.empty()) {
    if (base::ReadFileToString(base::FilePath(cert_path), &file_data)) {
      auto module = model->cert_db()->GetPrivateSlot();
      rv = model->ImportFromPKCS12(module.get(), file_data, password, true,
                                   &imported_certs);
      if (imported_certs.size() > 1) {
        auto it = imported_certs.begin();
        ++it;  
        for (; it != imported_certs.end(); ++it)
          rv &= model->SetCertTrust(it->get(), net::CA_CERT,
                                    net::NSSCertDatabase::TRUSTED_SSL);
      }
    }
  }
  return rv;
}
#endif
void OnIconDataAvailable(util::Promise promise, gfx::Image icon) {