* 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
v8::Local<v8::Value> val,
                     JumpListCategory* out) {
    mate::Dictionary dict;
    if (!ConvertFromV8(isolate, val, &dict))
      return false;
    if (dict.Get("name", &(out->name)) && out->name.empty())
      return false;
    if (!dict.Get("type", &(out->type))) {
      if (out->name.empty())
        out->type = JumpListCategory::Type::TASKS;
      else
        out->type = JumpListCategory::Type::CUSTOM;
    }
    if ((out->type == JumpListCategory::Type::TASKS) ||
        (out->type == JumpListCategory::Type::CUSTOM)) {
      if (!dict.Get("items", &(out->items)))
        return false;
    }
    return true;
  }
};
template <>
struct Converter<JumpListResult> {
  static v8::Local<v8::Value> ToV8(v8::Isolate* isolate, JumpListResult val) {