* 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
content::WebContents* web_contents,
    net::SSLCertRequestInfo* cert_request_info,
    net::ClientCertIdentityList identities,
    std::unique_ptr<content::ClientCertificateDelegate> delegate) {
  std::shared_ptr<content::ClientCertificateDelegate> shared_delegate(
      delegate.release());
  
  
  auto client_certs = net::CertificateList();
  for (const std::unique_ptr<net::ClientCertIdentity>& identity : identities)
    client_certs.push_back(identity->certificate());
  auto shared_identities =
      std::make_shared<net::ClientCertIdentityList>(std::move(identities));
  bool prevent_default =
      Emit("select-client-certificate",
           WebContents::FromOrCreate(isolate(), web_contents),
           cert_request_info->host_and_port.ToString(), std::move(client_certs),
           base::BindOnce(&OnClientCertificateSelected, isolate(),
                          shared_delegate, shared_identities));
  
  if (!prevent_default) {
    scoped_refptr<net::X509Certificate> cert =
        (*shared_identities)[0]->certificate();
    net::ClientCertIdentity::SelfOwningAcquirePrivateKey(
        std::move((*shared_identities)[0]),
        base::BindRepeating(&GotPrivateKey, shared_delegate, std::move(cert)));
  }
}
void App::OnGpuInfoUpdate() {