* 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::RenderFrameHost* opener,
    const GURL& opener_url,
    const GURL& opener_top_level_frame_url,
    const url::Origin& source_origin,
    content::mojom::WindowContainerType container_type,
    const GURL& target_url,
    const content::Referrer& referrer,
    const std::string& frame_name,
    WindowOpenDisposition disposition,
    const blink::mojom::WindowFeatures& features,
    const std::vector<std::string>& additional_features,
    const scoped_refptr<network::ResourceRequestBody>& body,
    bool user_gesture,
    bool opener_suppressed,
    bool* no_javascript_access) {
  v8::Locker locker(isolate());
  v8::HandleScope handle_scope(isolate());
  content::WebContents* web_contents =
      content::WebContents::FromRenderFrameHost(opener);
  if (web_contents) {
    auto api_web_contents = WebContents::From(isolate(), web_contents);
    
    if (!api_web_contents.IsEmpty()) {
      api_web_contents->OnCreateWindow(target_url, referrer, frame_name,
                                       disposition, additional_features, body);
    }
  }
  return false;
}
void App::AllowCertificateError(