HttpClientHandler.cs
HttpClientHandler.Legacy.cs
IMonoHttpClientHandler.cs
MonoWebRequestHandler.cs

../../../external/corefx/src/System.Net.Http/src/System/Net/Http/SocketsHttpHandler/CancellationHelper.cs
../../../external/corefx/src/System.Net.Http/src/System/Net/Http/SocketsHttpHandler/ConnectHelper.cs