* 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
if (HasSingleInstanceLock())
    return true;
  base::FilePath user_dir;
  base::PathService::Get(DIR_USER_DATA, &user_dir);
  auto cb = base::BindRepeating(&App::OnSecondInstance, base::Unretained(this));
  process_singleton_.reset(new ProcessSingleton(
      user_dir, base::BindRepeating(NotificationCallbackWrapper, cb)));
  switch (process_singleton_->NotifyOtherProcessOrCreate()) {
    case ProcessSingleton::NotifyResult::LOCK_ERROR:
    case ProcessSingleton::NotifyResult::PROFILE_IN_USE:
    case ProcessSingleton::NotifyResult::PROCESS_NOTIFIED: {
      process_singleton_.reset();
      return false;
    }
    case ProcessSingleton::NotifyResult::PROCESS_NONE:
    default:  
      return true;
  }
}
void App::ReleaseSingleInstanceLock() {
  if (process_singleton_) {
    process_singleton_->Cleanup();
    process_singleton_.reset();
  }
}
bool App::Relaunch(mate::Arguments* js_args) {