* 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 std::string& type,
                                    const base::DictionaryValue& user_info) {
  if (Emit("update-activity-state", type, user_info)) {
    *prevent_default = true;
  }
}
void App::OnNewWindowForTab() {
  Emit("new-window-for-tab");
}
#endif
void App::OnLogin(scoped_refptr<LoginHandler> login_handler,
                  const base::DictionaryValue& request_details) {
  v8::Locker locker(isolate());
  v8::HandleScope handle_scope(isolate());
  bool prevent_default = false;
  content::WebContents* web_contents = login_handler->GetWebContents();
  if (web_contents) {
    prevent_default =
        Emit("login", WebContents::FromOrCreate(isolate(), web_contents),
             request_details, *login_handler->auth_info(),
             base::BindOnce(&PassLoginInformation,
                            base::RetainedRef(login_handler)));
  }
  
  if (!prevent_default)
    login_handler->CancelAuth();
}
bool App::CanCreateWindow(