Add OkNegotiatedContentResult Class to the project

Here is the https://msdn.microsoft.com/en-us/library/dn308866%28v=vs.118%29.aspx I want. I plan use OkNegotiatedContentResult<T> Class in my project. How?

My project.json file

{"version": "1.0.0-*","dependencies": {"NETStandard.Library": "1.5.0-rc2-24027","xunit": "2.1.0","Moq": "4.5.8","dotnet-test-xunit": "1.0.0-rc2-build10025"
  },"testRunner": "xunit","frameworks": {"net451": {"imports": ["dotnet5.6","dnxcore50","portable-net45+win8","netcoreapp1.0"
      ]
    }
  }
}

Thanks.