* 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
.SetMethod(
          "invalidateCurrentActivity",
          base::BindRepeating(&Browser::InvalidateCurrentActivity, browser))
      .SetMethod("updateCurrentActivity",
                 base::BindRepeating(&Browser::UpdateCurrentActivity, browser))
      
      .SetMethod("moveToApplicationsFolder", &App::MoveToApplicationsFolder)
      .SetMethod("isInApplicationsFolder", &App::IsInApplicationsFolder)
#endif
#if defined(OS_MACOSX) || defined(OS_LINUX)
      .SetMethod("setAboutPanelOptions",
                 base::BindRepeating(&Browser::SetAboutPanelOptions, browser))
      .SetMethod("showAboutPanel",
                 base::BindRepeating(&Browser::ShowAboutPanel, browser))
#endif
#if defined(OS_MACOSX) || defined(OS_WIN)
      .SetMethod("showEmojiPanel",
                 base::BindRepeating(&Browser::ShowEmojiPanel, browser))
      .SetProperty("accessibilitySupportEnabled",
                   &App::IsAccessibilitySupportEnabled,
                   &App::SetAccessibilitySupportEnabled)
#endif
#if defined(OS_WIN)
      .SetMethod("setUserTasks",
                 base::BindRepeating(&Browser::SetUserTasks, browser))
      .SetMethod("getJumpListSettings", &App::GetJumpListSettings)
      .SetMethod("setJumpList", &App::SetJumpList)
#endif
#if defined(OS_LINUX)
      .SetMethod("isUnityRunning",