* 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/browser.h
bool RemoveAsDefaultProtocolClient(const std::string& protocol,
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    bool opened_at_login = false;
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    base::string16 path;
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    LoginItemSettings();
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    LoginItemSettings(const LoginItemSettings&);
  };
  void SetLoginItemSettings(LoginItemSettings settings);
  LoginItemSettings GetLoginItemSettings(const LoginItemSettings& options);
#if defined(OS_MACOSX)
  
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