* 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
static_cast<AtomBrowserClient*>(AtomBrowserClient::Get())
      ->set_delegate(nullptr);
  Browser::Get()->RemoveObserver(this);
  content::GpuDataManager::GetInstance()->RemoveObserver(this);
  content::BrowserChildProcessObserver::Remove(this);
}
void App::OnBeforeQuit(bool* prevent_default) {
  if (Emit("before-quit")) {
    *prevent_default = true;
  }
}
void App::OnWillQuit(bool* prevent_default) {
  if (Emit("will-quit")) {
    *prevent_default = true;
  }
}
void App::OnWindowAllClosed() {
  Emit("window-all-closed");
}
void App::OnQuit() {
  int exitCode = AtomBrowserMainParts::Get()->GetExitCode();
  Emit("quit", exitCode);
  if (process_singleton_) {
    process_singleton_->Cleanup();
    process_singleton_.reset();
  }
}
void App::OnOpenFile(bool* prevent_default, const std::string& file_path) {