* 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,
    int cert_error,
    const net::SSLInfo& ssl_info,
    const GURL& request_url,
    bool is_main_frame_request,
    bool strict_enforcement,
    bool expired_previous_decision,
    const base::RepeatingCallback<void(content::CertificateRequestResultType)>&
        callback) {
  v8::Locker locker(isolate());
  v8::HandleScope handle_scope(isolate());
  bool prevent_default = Emit(
      "certificate-error", WebContents::FromOrCreate(isolate(), web_contents),
      request_url, net::ErrorToString(cert_error), ssl_info.cert, callback);
  
  if (!prevent_default)
    callback.Run(content::CERTIFICATE_REQUEST_RESULT_TYPE_DENY);
}
void App::SelectClientCertificate(