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Tcp Connection Leak in CLOSED_WAIT when GZIpEnabled is set on TranslateService

See original GitHub issue

When using the Google.Apis.Translate.v2 package and creating and disposing TranslateService instances we have noticed a leak of IPv4 connections.

Minimal reproduction:

using System;
using System.Linq;
using System.Net;
using System.Threading.Tasks;
using Google.Apis.Services;
using Google.Apis.Translate.v2;

namespace Churyumov
{
    class Program
    {
        private static readonly NetworkCredential s_clientIdentity =
            new NetworkCredential(
                "<YOUR>",
                "<CREDENTIALS>");
        private static readonly string[] s_foreignText =
            new[]
            {
                "The quick brown fox jumps over the lazy dog",
                "Le renard brun rapide saute sur le chien paresseux",
                "Der schnelle braune Fuchs springt über den faulen Hund"
            };

        static async Task Main(string[] args)
        {
            var initializer = new BaseClientService.Initializer
            {
                ApplicationName = s_clientIdentity.UserName,
                ApiKey = s_clientIdentity.Password,
                GZipEnabled = true // << changing this to `false` prevents the leak 
            };

            using (var service = new TranslateService(initializer))
            {
                var request = service.Detections.List(s_foreignText);
                var response = await request.ExecuteAsync(default);
                foreach (var result in response.Detections)
                {
                    Console.WriteLine(string.Join(", ", result.Select(r => r.Language)));
                }
            }
            
            Console.WriteLine("Check open connections here!");
        }
    }
}

<Project Sdk="Microsoft.NET.Sdk">

  <PropertyGroup>
    <OutputType>Exe</OutputType>
    <TargetFramework>netcoreapp2.2</TargetFramework>
    <RootNamespace>Churyumov</RootNamespace>
    <LangVersion>Latest</LangVersion>
  </PropertyGroup>

  <ItemGroup>
    <PackageReference Include="Google.Apis.Translate.v2" Version="1.40.0.875" />
  </ItemGroup>

</Project>

When inspecting the application on the Check open connections here line with lsof you can see the connection to the Google translate service has not been disposed:

$ lsof -p `pgrep dotnet` | grep IPv
dotnet  57839 willspeak   52u    IPv4 0xd178e425407bd7f9       0t0        TCP 10.11.1.61:50431->lhr48s08-in-f10.1e100.net:https (ESTABLISHED)

It looks like the TwoWayDelegatingHandler created when the GZipEnabled option is set to true doesn’t properly dispose of an inner handler:

Screenshot 2019-06-05 at 17 04 12